A three-year-old virus may damage some PCs Thursday when it's set to strike again.
Known as CIH, or the more dire-sounding Chernobyl, the virus first hit a month after the Melissa virus three years ago and is due to strike on Thursday.
Antivirus software company Trend Micro warned that though the outbreak may not be severe or widespread, CIH can nevertheless wreak havoc on a computer's hard disk by deleting the information the disk needs to find files.
CIH is an old file infector that originated in Taiwan and was discovered in June 1998. The writer, Chen Ing-Hau, created the virus while he attended university in the island nation.
It struck an estimated as 700,000 to 1 million PCs worldwide on April 26, 1999, with high incidences of infection in Asia, the Middle East and Eastern Europe. Very few of those incidents have been verified, however.
Although the number of CIH cases fell sharply in April last year, it still caused considerable damage.
It infects only Windows 95 and Windows 98 systems and activates when the system month reads April and the system day reaches 26. When one antivirus company noticed that the date coincided with the anniversary of the Chernobyl nuclear plant accident, it dubbed the virus "Chernobyl".
When CIH triggers, it tries to overwrite critical information on the system's hard disk and, on some computers, deletes system information storied in BIOS memory, which leaves the computer unbootable.
Some variants of this virus are triggered on the 26th day of other months.
ZDNet News' Robert Lemos reported from San Francisco, and staff writer Irene Ang reported from Singapore.
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