Computer Viruses -
Learn more about the threats to your PC
Any computer connected to the internet faces a daunting range of electronic threats. Perhaps the biggest single threat to any computer is the humble software bug. Seemingly innocuous programming errors can be exploited to force entry into a computer and also provide the weak spots that allow computer worms and viruses to proliferate.
Many software bugs will simply cause a computer to crash. But an expert programmer can sometimes figure out how to make a computer malfunction in a creative way, so that it provides access to secure parts of a system, or shares protected data.
Viruses and worms
A computer virus is a program that spreads between computers by hiding itself within a - seemingly innocent - document or application. A worm, on the other hand, is a program that replicates and travels without "infecting" anything else on a system.
The first worms appeared in the 1970s and spread slowly between computers connected to the same network. They simply displayed an annoying message on the screen of each infected machine. The first computer virus, called Elk Cloner, was written in 1982 and infected computers via floppy disks.
Trojans and zombies
But viruses and worms no longer just provide a way for malevolent hackers to gain notoriety. Today's viral code can contaminate computers at lightning speed, spreading via email, peer-to-peer file-sharing networks and even instant messaging programs. The most successful ones cause serious damage, forcing companies around the globe to close down while infected computers are cleaned up.
Spam, Spam, Spam
Spammers have also begun using botnets to forward unsolicited bulk email advertising, or spam, through scores of zombie PCs. This makes it far more difficult for spam hunters to block the messages at source and catch the culprits. To combat computer scientists' best efforts to stem the tide of junk email, the spammers have had to become more cunning and sophisticated. More recently, spim (spam by instant messenger) and spit (spam by internet telephony) have joined the fray.
Spam's more sinister cousin is the phishing email. This is a con trick that arrives as an email and tries to trick a recipient into handing over money or sensitive personal information like their bank account details or a username and password.Some genuine sites have even proven vulnerable to software glitches that can be exploited to capture information from regular users. Phishing is especially threatening because it can be used to steal a person's digital identity.
Along with spam and phishing, spyware represents the third of an unhappy trinity of internet pests. These insidious and clandestine programs typically find their way onto a computer system alongside another, often free, software application, although some can also exploit software bugs to get onto a machine. The programs are used to serve up unwanted adverts, change system settings and gather information on a user's online behaviour for marketing purposes.
The term "computer hacker" was first coined in the 1960s and originally meant someone capable of developing an ingenious solution to a programming problem. But the phrase has since fallen into disrepute, entering the popular vocabulary as a term for a programmer with criminal intent. There are many tools in the modern hacking kit, including network scanners, packet sniffers, rootkits and decompilers. But "social engineering" - for example, putting a particularly enticing message in an email header to encourage people to open it - and even search engines can also be useful weapons for the hacker.
As the number of computers networks has grown, so have the possibilities for more serious misuse. And, as money increasingly becomes a digital commodity, the world has seen the emergence of serious computer criminals. Criminal gangs have also started to get in on the action, attracted by the huge quantities of money now spent online every day. There is evidence that unscrupulous experts can also earn serious money from crime syndicates by breaking into computer systems, writing viruses and creating phishing scams.
And it is not just ordinary desktop computers that are under threat. Governments, banks and critical infrastructure can also be brought to a standstill by an expert armed only with a laptop computer and a net connection.