Sunday, April 25, 1999 Published at 09:25 GMT 10:25 UK
Deadly virus warning
CIH virus can corrupt computer's data (Courtesy Datafellows.com)
Computer users across the world are on alert for a malicious virus that is due to strike on Monday.
It is also called the Chernobyl virus because it is timed to go off on the anniversary of the Russian nuclear accident, one of technology's worst disasters.
This can cause complete loss of data, and possibly render the computer unusable.
Risk to W95/W98 users
Users of DOS, Windows, Windows NT or Macintosh users are not at risk from CIH. It only replicates and activates under Windows 95 and Windows 98.
But most up-to-date anti-virus software will spot it. There are various free checking programs that can be downloaded from the Internet to scan a computer for the bug.
The virus was first located in Taiwan in early June 1998 and then spread to the wider world.
It has been among the 10 most common viruses for several months, spreading very quickly as it has been distributed through pirated software and the Internet.
It is not widespread in Europe or the US, but very common on computers in Asia. CIH is a program, so it must be activated before it can take effect.
"There would be no way of knowing that you had downloaded this virus and run it, it's completely invisible to the user," said virus expert Mikko Hypponen of software company DataFellows.
The CIH virus is far more dangerous to individual computers than Melissa, the much-publicised macro bug that spread relatively benign problems far and wide on the Internet last month.
Melissa was mainly spread by e-mail, and relied on people opening a document attached to e-mail messages.