An Introduction To Computer Viruses

A beginner’s guide to computer viruses – what they are, why they matter, and how to avoid them…

A computer virus is a piece of software code that has been designed to spread from one device to another. Its content is usually harmful; viruses typically corrupt programs, steal sensitive data or even seize control of a device altogether. Like their biological cousins, computer viruses replicate from a single source, using each infected host as a springboard to reach an ever-widening circle of victims.

The history of viruses

The first documented computer virus was created in 1981, and ironically, it targeted Apple computers with the Apple II Elk Cloner. Although the coding didn’t cause significant damage, it introduced the concept of malicious software, or malware, to the world. Within five years, the first viruses had been detected in mainframe computers, MS-DOS-powered equipment and manufacturer-specific machines. Most modern viruses target Microsoft-powered devices, since the sheer number of subtly different Linux and Unix operating systems makes it difficult for a virus to spread very far on these formats. However, all devices and operating systems are at risk to some extent.

Virus or worm?

Although viruses and worms typically conduct the same unwarranted invasion of a host computer, their method of transmission is different. Viruses are hidden inside programs or files, unleashing their payload when the infected program/file/attachment is opened or executed. They are usually destructive in nature, performing tasks such as stealing personal information or distributing spam mail.

Worms can travel independently across the internet or a local area network from host to host, and they are increasingly taking over from viruses. Although some worms carry damaging payloads, their primary aim is often to commandeer processing power or bandwidth in order to self replicate and infect other devices.

Symptoms of infection

With a myriad of different viruses and worms roaming around cyberspace, it’s difficult to pinpoint obvious symptoms of infection. However, common signs of a virus or worm being present include:

• A device runs slowly because its memory and processing power are being used for malicious purposes
• Strange messages are displayed on-screen which can’t be removed or deleted
• Peripherals stop operating properly
• A sudden inability to access the internet or email packages
• Antivirus software fails to work
• Internet browser may be changed to default to a new home page or a specific search engine.

Pre-emptive measures

The first precaution against malware should be a trusted antivirus package which will constantly scan the computer’s activity and vet every file that is downloaded or received via email. Some free antivirus packages are as good as their paid-for counterparts, and regular updates will ensure they have the latest information about newly-created viruses. These can usually be identified from unique strings of code contained within each virus.

Alongside regular software backups, common sense is also vital. Never open email attachments from unknown senders, and don’t click on files with the .exe suffix unless you trust the source (e.g. a software download from a reputable website). Message boards are particularly prone to hosting malware, so stick to high-profile forums and navigate away from a website if your internet browser suggests it might be unsafe to continue.

Reactive measures

An infected computer may be hard to identity unless the virus explicitly announces its presence. Many conceal themselves to avoid detection, and some can actually resist attempts to destroy them. Zombie systems, controlled remotely through vast botnets are responsible for some of the most damaging co-ordinated attacks in recent internet history and may be identifiable due to strange behaviour such as powering on by itself, refusal to open certain programs, changed search engine, very slow loads times, high drive activity and high processor use.

Antivirus software may struggle to identify the malware once it’s embedded, but dedicated malware programs like Spybot S&D or Norton Power Eraser can often eradicate unwanted items – be aware however that the latter may inadvertently damage legitimate programs. Computer specialists can sometimes remove malware, often by performing a full-format erase of a device’s hard drive and effectively resetting its factory defaults. This underlines the importance of regularly backing up personal data, since malware can attack at any time.