Called "Boza", the virus can corrupt programs so that they no longer function, occasionally putting up a message on the screen saying: "The taste of fame just got tastier! VLAD Australia does it again with the world's first Win95 virus." It can then spread to other users' machines.
This poses a new threat to the 10 million users of the product, which was launched in a blaze of publicity last August and became the fastest- selling software program ever.
"Boza will probably go down in history," says Paul Ducklin, an analyst for Sophos, a software company based in Abingdon, Oxfordshire, which specialises in writing programs to seek and destroy viruses. "It's the first that we've seen that affects Windows 95 programs in particular."
Virus attacks, and protecting companies from their effects, have turned into big business since the first one - called "Brain" - was discovered in 1988. Now, hundreds are found every month. Market research suggests that in 1994, virus infections cost British business pounds 128m - including loss of data, work time, and effort to repair any damage.
Boza's makers, whose identity is unknown but who are assumed to be Australian, have clearly targeted the new Microsoft system. Windows 95 differs from Microsoft's previous operating systems because it can run programs whose instructions are 32 bits long, rather than 16 bits - allowing greater flexibility. Boza is written specifically to infect 32-bit programs. It attaches itself to existing programs and, while they run, makes copies of itself which are then attached to other programs.
When Microsoft launched Windows 95, many analysts criticised it for not including an anti-virus program. Now their fears have been vindicated, specialist companies will have to incorporate tests for the new virus into existing protective software. But experts take some comfort from the fact that Boza is not especially easy to spread.
"If you run a program that's infected with Boza, then it will infect up to three more programs," says Alan Solomon, chairman of S+S International, based in Aylesbury, Buckinghamshire. "But to infect someone else's machine, you would have to give them an infected program, and they would have to run it. Most people don't swap programs around like that."
More dangerous viruses lurk on floppy disks and spread when the user inserts the disk in another computer.
But Dr Solomon says that some people overreact when they find that their machine has been infected with a virus. "An infection should only cost a few dozen pounds per computer, if you add up the time and effort," he says. "Unless you get it wrong. In that case the sky's the limit. Some people start doing wild things to their machines which are the computing equivalent of scrapping a car because the ashtray's full."
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