In India, the Chernobyl virus that first struck on April 26, caused far more damage than the Melissa virus that had struck in May, say industry observers like Kerrie Turner of Symantec, which provides the Norton AntiVirus software in the country.

The virus infects Windows 95 and 98 executable files, which are basically 32-bit programmes. Several corporates and home users using these programmes were known to have been hit by the virus.

In today's networked world, the internet is a major cause for a concern. Recently in the US, free-downloadable virus scannerscaused havoc with data files. The e-mail came in the form of an electronic cold call from a sales agent working for a software company trying to drum up business by offering a free virus scanner on a trial basis.

The company promptly denied that their staff was sending random e-mail messages offering free trials of virus scanner software from its site.It later turned out to be a hacker masquerading as an agent of this anti-virus company, who first spoofed this website address and distributed a computer virus within software wrongly attributed to its product line.The history of CIH takes it all the way to Taiwan, where a computer expert Chen Ing-Hau (CIH) is believed to have written the virus. As per records, the virus targets dates of 26 of any month and has the potential to erase hard drives and corrupt a PC's BIOS.

If an infected programme is run, the virus quickly spreads into the computer's memory and then attempts to modify or corrupt certain types of Flash BIOS, the software that initialises andmanages relationships and data flow between the system devices, including the hard drive, serial and parallel ports and the keyboard. By overwriting part of the BIOS, CIH can keep a computer from starting up when power is turned on.

Nortone has a developed a fix -- kill--cih.exe tool -- which also assists other anti-virus solution users to clear their networks or machines infected with the latest variant of the CIH virus. The software can be run from either the DOS command line or from a log-in scrip, allowing administrators to automate the disinfection process.

Another virus which struck was Worm.ExploreZip, which erases files on a PC. The worm e-mail goes out as an attachment with the filename zipped -- files.exe in reply to unread messages you usually find in your Inbox. Once it responds to a message in your Inbox, it will mark it so as not to respond to the message again. The e-mail message sent may appear to come from a previously known e-mail writer in response to a previously sent e-mail. Thise-mail will say "I received your e-mail and I shall send you a reply ASAP. Till then, take a look at the attached zipped docs."