Ways That Computer Viruses Spread

For a virus or similar program to have any great impact it needs to be able to spread from one machine to another. They are specifically designed to get access to parts of your computer system that allow for communication with other machines. Below is a discussion of some of the most common methods.

Boot Infectors

Every disk (hard disk, floppy, CD, DVD) contains a boot sector whether it is a bootable disk or not. When a computer is turned on, it looks for boot informati...


For a virus or similar program to have any great impact it needs to be able to spread from one machine to another. They are specifically designed to get access to parts of your computer system that allow for communication with other machines. Below is a discussion of some of the most common methods.

Boot Infectors

Every disk (hard disk, floppy, CD, DVD) contains a boot sector whether it is a bootable disk or not. When a computer is turned on, it looks for boot information. If the computer finds a disk with boot information, it reads that information and uses it to properly start the computer. If for some reason that boot information is infected with a virus, the virus is activated and possibly transferred to the computer's hard drive (if the infection was on a CD for example).

Once the boot code on the hard drive is infected the virus will be loaded into your computer's memory every time you start your computer. From memory the boot virus can travel to any and every disk that is put into your computer. This is how the infection spreads.

Most boot viruses could be on a system for a long time without causing problems, simply existing there to spread themselves. Often such viruses are designed to activate their bad behaviour on a specific date (Halloween for example). There are some nasty boot viruses that will destroy the boot information or force a complete format of the hard drive immediately after they get into a computer.

Program Infectors

When an infected application is run the virus activates and is loaded into memory. While the virus is in memory any new program file that you run can become infected. This means that there will be increasingly more applications on your system that are infected. Multiple infections are very common and will certainly cause system problems.

Program files may function without any problems for some time but eventually they will have problems or multiple infections brings the entire computer system down. The data the program produces may be a first sign of infection such as saving files without proper names, or with incorrect/incomplete data being saved.

Viruses of this type are often designed to seek out programs that are used to share information between users/computers such as email applications, screen savers, office document Macros, and self-extracting compressed files.

Through e-mail attachments

Many of the most dangerous viruses are primarily spread through e-mail attachments - files that can be sent along with an e-mail message. In such cases, the user of an infected computer unknowingly attaches an infected file to an email message, and then sends the email to a friend or colleague. When the email is received, the virus is launched when the file attachment is opened, thus infecting a new computer. Email messages with animations, automated greeting cards, jokes, photographs, spreadsheet and document files, all have been documented to contain virus files.

More and more frequently these days mass mailing email worms/viruses are being released. These attacks AUTOMATICALLY scan your computer's files for any email address it can find and then uses your email application to AUTOMATICALLY send infected messages to any email address found in any file on your computer (not just email message files).

It is important to be aware of the emails that you open to make sure that they do not contain harmful viruses. Even emails from family and friends could have a virus, if that person's computer is infected. This is where an anti-virus software would be really helpful in detecting if there is a virus in any incoming messages.

How Viruses Contaminate Your Computer

Viruses are little bits of software that normally have a negative impact on our computers when they are activated. Usually viruses are attached onto other software programs (games, disk utilities, office documents/Macros, screen-savers), and are activated when these normally harmless programs are started.

A virus is inactive until the infected program is run or an infected boot record on a floppy/CD is read. When the virus is activated it loads into your computer's memory ...

Viruses are little bits of software that normally have a negative impact on our computers when they are activated. Usually viruses are attached onto other software programs (games, disk utilities, office documents/Macros, screen-savers), and are activated when these normally harmless programs are started.

A virus is inactive until the infected program is run or an infected boot record on a floppy/CD is read. When the virus is activated it loads into your computer's memory where it can perform its nasty job or spread itself to other programs on your system or computers in your network.

Floppy disks used in an infected system (or CD-Roms/DVDs burned on an infected system) can then carry the virus to another machine. Programs downloaded from USENET, or file-sharing programs (Kazaa, Morpheus, Limewire etc.) can also spread a virus. More frequently now, email is also becoming a favourite way to spread viruses, Trojan horses and especially internet worms.

It should be made clear, that USENET and file-sharing programs do not create viruses or infected files in any way. It is certain anti-social people who create viruses, and then use these services to spread the infected files to other users on the system.

This is very similar to cars and highways in that Ford, Toyota or the highway makers do not cause traffic accidents, it is the idiot who got drunk and then drove who causes a 14 car pileup. Of course if there weren't cars or highways there wouldn't be an accident... then again, the idiot would still be getting smashed and driving his horse-carriage into the store window.

When you get a virus on your computer, it can erase everything that you have on your hard drive. Each virus is different - some of them come up as strange messages on your screen, while others just work at eroding the files on the computer. A virus just doesn't appear in your computer - you have to put them there, usually by running program from the Internet that contain viruses. They sometimes come from attachments in emails. It is possible that an email from a friend could contain a virus if that person's computer is infected. With anti-virus software installed on your computer, this will tell you whether or not it is safe to open the email with a message such as "No virus detected in incoming mail:

When you do get a virus through programs or mail, it hides in your computer and when you save data in the computer, you also save the virus. Then it starts to infect all the other files in your computer. When you send files to a friend or co-worker, you also send the virus to his/her computer. After a while the virus starts to crowd the data in your files and causes major problems with the system, such that you may not even be able to open important documents or you may not be able to open any of the programs on the computer. The virus won't affect the memory of your computer, but it will affect any disks that you use to save your work.

How To Keep Your Computer From Spreading Viruses

There are some simple steps you must take to avoid becoming a victim of computer viruses and also stop from spreading viruses to others. Here are some things that you can and should do.
Email Issues to watch

Never open an E-mail with an attachment you were not expecting.

The latest batch of virus programs are often spread by E-mail. Even if your anti-virus program does not warn you about the attached file and even if the eMail appears to come from someone you know, do ...

There are some simple steps you must take to avoid becoming a victim of computer viruses and also stop from spreading viruses to others. Here are some things that you can and should do.
Email Issues to watch

Never open an E-mail with an attachment you were not expecting.

The latest batch of virus programs are often spread by E-mail. Even if your anti-virus program does not warn you about the attached file and even if the eMail appears to come from someone you know, do not open it if you were not expecting it, and if you were expecting it, only open it AFTER scanning it with your up-to-date virus software.

Scan ALL incoming email attachments (regardless of who sent it).

Be sure to run each attachment you plan to open through the anti-virus check. Do this even if you recognize and trust the sender; malicious code, like Trojan horses, can slip into your system by appearing to be from a friendly source.
Turn off the 'automatic preview' in your email program.

Automatically previewing an email message has the exact same effect as opening and reading an email. My of the newest internet worms, trojans, and viruses simply need to have an email message read in order for them to be activated. Turning off the preview feature allows you to scan any email BEFORE you actually read it.

Disk Issues to watch

Don't boot from a floppy disk.

Floppies are one of the most common ways viruses are transmitted. If you are using a floppy while working on your computer, remove it when you shut the machine off or the computer will automatically try to boot from the floppy, perhaps launching any viruses on the disk.

Web Based Issues

Keep your web browser set to its highest security level.

Its a pain to get the warning messages on every other web page you visit, but its the best way to protect yourself - especially if you use Microsoft Internet Explorer and Outlook.

Don't download programs from the Web.

Unreliable sources such as Internet newsgroups or Web sites that you haven't heard of may be willing providers of viruses for your computer. Avoid downloading files you can't be sure are safe. This includes freeware, screensavers, games, and any other executable program - any files with an ".exe" or ".com" extension, such as "coolgame.exe." Check to see if the site has anti-virus software running on their side. If you do have to download from the Internet, be sure to scan each program before running it. Save all downloads to one folder, then run virus checks on everything in the folder before using it. Regardless of where you download from, ALWAYS scan downloaded software.

Routine Maintenance

Make regular back ups of important data

Make it a habit to back up all of your most important files at least once a month. Store the back up discs in a safe place.

Clean any virus/worm/trojan off your computer
(Details: http://www.antivirus-report.com/trojan-horse-removal.html )

Using your antivirus software, perform a full system scan of your PC, hopefully it will detect and remove the virus. If a virus was detected, restart your computer and run the full scan again. Sometime the virus will keep reappearing, due to the evolving nature of viruses. Symantec is particularly fast at providing removal tools should you ever get a virus or worm infesting your computer.

What is a removal tool? Well simply put it is a simple software that will scan your computer for infections, and then remove them from your machine. You most often need this if your machine got infected BEFORE you installed antivirus software.

Top Considerations for PC Protection

And the final and most important two things to do to keep your computer clean and make sure it does not spread viruses to other computers...

Install a Firewall

If you use a broadband/high-speed method to access the internet, you need to get a firewall. A firewall is a program that defends your computer from hackers who attempt to gain direct access to your computer over the Internet. There is a very good firewall program called ZoneAlarm that will do the trick if you use Windows.

Install and use a high-quality anti-virus program.

This is the key to protecting your computer. Buy one of the major anti-virus programs - Norton Anti-Virus, PC-Cillin, or McAfee Anti-Virus. The primary benefit of the commercial packages is the frequency and ease of updating the virus definition files that these programs use to detect viruses. With new viruses popping up all the time, unless your protection software is kept updated, you start to become ever more vulnerable to infection.

Get immediate protection.

Configure your anti-virus software to launch automatically on start-up and run at all times. This will provide you back-up protection in case you forget to scan an attachment, or decide not to. And in case you forget to load up your anti-virus software, configuring it to start by itself will ensure you get immediate protection anyway. The top antivirus software programs all do this (but only if you have one installed on your computer). You do have current antivirus software installed right? If not, you can go to this page for more information on why you need antivirus software and how easy it is to use.

About Norton Anti-Virus

With the many types of anti-virus software, it is helpful to read a brief description of what the different types do and how they can be beneficial to you and your computer.

Norton Anti-virus

Symantec's Norton AntiVirus software is perhaps the world's most trusted antivirus solution. It is available for both Windows PC's, and Macintosh (Symantec Antivirus for Macintosh - S.A.M). Norton AntiVirus is a very reliable and easy-to-use anti-virus product. It's the best anti-...


With the many types of anti-virus software, it is helpful to read a brief description of what the different types do and how they can be beneficial to you and your computer.

Norton Anti-virus

Symantec's Norton AntiVirus software is perhaps the world's most trusted antivirus solution. It is available for both Windows PC's, and Macintosh (Symantec Antivirus for Macintosh - S.A.M). Norton AntiVirus is a very reliable and easy-to-use anti-virus product. It's the best anti-virus product for catching viruses in downloaded files and E-mail. Norton AntiVirus is also more expensive than McAfee VirusScan although not by much, and the added abilities of Norton can easily make up the difference.

Norton AntiVirus includes many tools that can be run in the background, including watching for suspicious PC activity and automatically checking downloaded files for viruses. Norton AntiVirus is also automatically configured to handle E-mail virus scanning for email messages coming into your computer, as well as those you send. This process automatically scans and cleans both incoming and outgoing email, stopping viruses from infecting your computer or spreading to others. It removes viruses automatically, without interrupting your work and prevents infections during real-time online chats, and also detects viruses in instant-message attachments. Because so many viruses and internet worms are now spread using email and Instant Message Systems, this is extremely valuable and necessary protection.

Norton Installation

Installation is simple. Simply install the CD in your CD drive, and the installer will launch automatically. The installer should ask you if you want to do a pre-install scan of your system for viruses. This is a very good thing to do. Once this is finished, the installation will proceed, and you can accept all the defaults without worry. Once the installation is complete, you'll be prompted to go online and get up-to-date virus definitions. DO NOT skip this step. Having up-to-date virus definitions is essential to the performance of any antivirus software.

Normal Use

Norton is a very hands-off program. Pretty much it is an install and forget program that looks after itself. It will automatically notify you if there is anything that you need to do. If a virus is found, the software will try to automatically repair the file, if it can't, it will place the file in a safe 'quarantine' zone, and let you know. In addition to looking for known viruses, the Norton Antivirus Bloodhound feature tries to spot new viruses and worms by their behaviour that is common to such nasty programs.

Checking your system and downloading updates are two things you need to do regularly. Norton Antivirus makes them painless by setting up a full system scan once a week and checking for new updates (both to the software, and virus definitions) whenever you're online. These simple update scans hardly slow down your PC down at all.

Overall, Norton Antivirus is an excellent way to guard against viruses. It is the system that I recommend to my clients most often, and that I use personally.