Viruses infect your system with two primary aims. The first goal is to hijack system resources to deliver some sort of payload. Their second objective is to replicate themselves. They can accomplish both missions in a wide variety of ways. Some viruses exist at your system’s most fundamental levels, infecting your boot sector and loading into memory each time the system starts. Others hide within operating system components, scripts embedded in applications, and even hidden files or fragments. They either target general performance, attempting to overload system resources, or they execute functionality that can range from taunting messages to complete file system destruction.

Less sophisticated viruses may break things in obvious ways or act primarily as nuisances. Advanced variants operate much more subtly, often without noticeable effects but with more severe eventual consequences. Viruses can shut down targeted programs, stop peripherals and components from working, wipe out data and settings, or eventually cause the collapse of your entire system.

How Viruses Spread

Understanding how viruses find an opening into your computer is the first step in becoming virus-free. Unfortunately, viruses have plenty of opportunities to spread and an abundance of delivery mechanisms (or vectors). Viruses can enter your system via infected files passed via memory sticks or other removable storage, from email messages or emailed file attachments, from other computers on a shared network, or even from malicious Web sites. Once on your system, viruses operate by riding along with legitimate programs, referred to as the host. When you open an infected application or script, the virus launches and either delivers its payload or seeks out other files to infect.

Viruses don’t always rely on blatant deception. Some of the most famous and damaging viruses have simply hitched a ride on otherwise legitimate word processor files, been embedded in regular Web pages, or even come installed on new hardware. You can’t evade every conceivable threat, but you should avoid dangerous practices that expose your system to unnecessary risk. Sharing network drives, opening files among public computers, opening email attachments from unknown sources, and downloading pirated software are all hazardous to your computer’s health.

Diagnose An Infection

Viruses are incredibly varied and emerge in different ways, so diagnosis is sometimes difficult. In fact, some viruses are nearly undetectable and do no obvious damage. You’re better off seeking out and eradicating even the most apparently restrained viruses, though, if for no other reason than to avoid providing a platform to spread infection. Your first and primary tool for diagnosing any viruses that find their way onto your system is to use regularly updated antivirus software. Scheduling regular virus scans (in addition to antivirus software updates) will help you discover malware before it becomes a problem. If you become infected with something between scans, or if a particularly wily virus slips through your defenses, a few indicators may help identify infections.

First, watch for erratic or unusual behavior lacking an immediate or apparent cause. Strange and new error messages, inexplicable system slowdowns, and sporadic reboots are all warning signs. When an application that has been working fine for ages starts acting up, start to suspect a virus. These warning signs should set off particularly urgent bells if they appear shortly after engaging in any risky behavior, such as installing a new freeware application, downloading media files from sketchy Web sites, or opening an email that didn’t do exactly what you thought it should. Go through your regular troubleshooting process to rule out less sinister possibilities, but the threat of virus infection shouldn’t be far from your mind.

Finding The Cure

Getting rid of computer viruses requires many of the same tools as protecting yourself from them in the first place. Reliable antivirus software is the key. For specific product information, refer to our antivirus software overview on page 63. In the meantime, we’ll give you a few tips on general practices to help clear up any nasty acquisitions. First, schedule automatic scans at least weekly. Second, make sure your antivirus software includes regular updates to its virus definitions and scanning engine so that it's continuously adapting to changing threats. This is usually part of the subscription package with any commercial antivirus product, but you should check periodically to make sure the updates install properly.

When viruses get through your defenses, take advantage of your antivirus software’s options first. Remove, repair, or quarantine infected files if offered. If that does not work, you can try Windows’ System Restore tool. Roll back to the last point before virus-related problems arose. To do so in both Windows XP and Windows Vista, click Start, open All Programs, click Accessories, click System Tools, and choose System Restore. Some viruses corrupt or disable restore points, though, so this option may not be available. In extreme cases, you may need to remove and uninstall infected applications or components, to the point of even reformatting and rebuilding the system. This is a corrective action of last resort, but one that you may have to take. It should go without saying that regular data backups—frequently scanned for viruses themselves—should be an integral part of every computing environment.

Viruses certainly aren’t the only threats to your computer, but they’re among the most prevalent. The good news is that you can defeat viruses with a little education, steady vigilance, and the right tools.

by Gregory Anderson