Type of computer viruses and how they work

• Worm: A virus designed to take control of a system temporarily. It often corrupts data and causes irreparable damage.

• Trojan horse: Usually disguised as a useful program that contains hidden instructions to perform a malicious task instead. A Trojan horse might even be disguised in the form of a game or a utility programmme to attract users. Only when the computer user run the programme will he realise that he has loaded a virus that may erase the data on the hard disk or cause another damage.

• Time bombs/logic bombs: They are designed to sit harmlessly on a system until a certain event or date causes the programme to activate itself. The most famous of which is the Michelangelo virus, named after the great artist

• File infectors: Most common virus that spreads from program to program and do damage to code, data, and directories. A file infector virus hidden on a floppy disk will transfer itself to any hard disk that the floppy disk comes into contact with. When another floppy disk is inserted into the computer containing that hard drive, the virus will copy itself onto that floppy disk.

• Boot sector virus: This sort of viruses will load each time the computer is booted and can isolate data stored on the disk