Viruses

There are many different ways to classify viruses, and each of these methods comes with its own set of colorfully-named categories. Worms, macroviruses, trojans and backdoors are some of the more well-known examples. Many of these viruses spread over the Internet, using email, malicious webpages or other means to infect unprotected computers. Others spread through removable media, particularly devices like USB memory sticks and external hard drives that allow users to write information as well as reading it. Viruses can destroy, damage or infect the information in your computer, including data on external drives. They can also take control of your computer and use it to attack other computers. Fortunately there are many anti-virus tools that you can use to protect yourself and those with whom you exchange digital information.

Anti-virus software

There is an excellent freeware anti-virus program for Windows called Avast, which is easy to use, regularly updated and well-respected by anti-virus experts. It requires that you register once every 14 months, but registration, updates and the program itself are all free-of-charge.

Clam Win is a FOSS alternative to Avast and the various well-known commercial anti-virus programs. Although it lacks certain features that are important for a primary anti-virus program, Clam Win has the advantage that it can be run from a USB memory stick in order to scan a computer on which you are not allowed to install software. This is extremely helpful when you have no choice but to use public computers or Internet cafes for sensitive work.

Tips on using anti-virus software effectively

• Do not run two anti-virus programs at the same time, as this might cause your computer to run extremely slowly or to crash. Uninstall one before installing another.
• Make sure that your anti-virus program allows you to receive updates. Many commercial tools that come pre-installed on new computers must be registered (and paid for) at some point or they will stop receiving updates. All of the software recommended here supports free updating.
• Ensure that your anti-virus software updates itself regularly. New viruses are written and distributed every day, and your computer will quickly become vulnerable if you do not keep up with new virus definitions. Avast will automatically look for updates when you are connected to the Internet.
• Enable your anti-virus software's 'always on' virus-detection feature if it has one. Different tools have different names for it, but most of them offer a feature like this. It may be called 'Realtime Protection,' 'Resident Protection,' or something similar. Take a look at Section 3.2.1 of the Avast Guide to learn more about that tool's 'Resident Scanner.'
• Scan all of the files on your computer regularly. You don't have to do this every day (especially if your anti-virus software has an 'always on' feature, as described above) but you should do it from time to time. How often may depend on the circumstances. Have you connected your computer to unknown networks recently? With whom have you been sharing USB memory sticks? Do you frequently receive strange attachments by email? Has someone else in your home or office recently had virus problems? For more information on how best to scan files, see the Avast Guide.

Preventing virus infection

• Be extremely cautious when opening email attachments. It is best to avoid opening any attachment received from an unknown source. If you need to do so, you should first save the attachment to a folder on your computer, then open the appropriate application (such as Microsoft Word or Adobe Acrobat) yourself. If you use the program's File menu to open the attachment manually, rather than double-clicking the file or allowing your email program to open it automatically, you are less likely to contract a virus.
• Consider the possible risks before inserting removable media, such as CDs, DVDs and USB memory sticks, into your computer. You should first check that your anti-virus program has the latest updates and that its scanner is running. It is also a good idea to disable your operating system's 'AutoPlay' feature, which can be used by viruses to infect your computer. Under Windows XP, this can be done by going inside My Computer, right-clicking on your CD or DVD drive, selecting Properties and clicking on the AutoPlay tab. For each content type, select the Take no action or Prompt me each time to choose an action options then click OK.
• You can also help prevent some virus infections by switching to free and open source software, which is often more secure, and which virus writers are less likely to target.