A new computer virus that spreads by e-mail and deletes files on the victim's machine is wreaking havoc on PCs and networks around the world.

The program, dubbed by some virus experts "ExploreZip.worm," deletes word-processing, spreadsheet and presentation files from hard drives. In some cases, the virus travels onto corporate computer networks and begins deleting files it encounters there as well.

It is a like a malicious cousin of the recent Melissa virus, which traveled by e-mail and tricked recipients into opening attached files that then released the program. Melissa's main damage was to send out copies of itself to the first 50 addresses atop a victim's e-mail address book, causing a massive e-mail traffic jam.

"It's more significant than the Melissa virus," said Sal Viveros of Network Associates, a company that tracks viruses and offers protection products. He said the company has been contacted by 25 large corporate customers with networks of thousands of computers, as well as "thousands and thousands" of smaller customers.

Users who discover the e-mail message on their machines should delete it without opening the file; free software that will scan the user's computer and eradicate the virus can be found on the Web sites of Network Associates (www.nai.com) and other anti-virus software makers.

The program was first detected Tuesday but reports mushroomed yesterday, said Mark Zajicek of the CERT Coordination Center, a federally funded response team that is part of the Carnegie Mellon University Software Engineering Institute.

The program, technically known as a "trojan horse," arrives in a victim's e-mail box and scans it for the address of the most recent incoming message. It then sends what looks like a reply to that message, containing the words "I received your email and I shall send you a reply ASAP. Till then, take a look at the attached zipped docs."

"It looks like they are getting a reply from you -- but you didn't send the reply, the worm did," Zajicek said. Double-clicking on the attached document sets the destructive program into action in one computer at a time.

One of the large corporations hit by the virus, jetliner maker Boeing Co., shut down e-mail services for all 160,000 computers in its network once it became clear that the early alerts sent out via e-mail and the company's internal Web site had not stopped the program.

Boeing spokesman David Suffia said that "only a tiny fraction" of the company's computers were infected, but, as at a day-care center with a single case of head lice, quick and decisive action is necessary to stop the problem before the problem becomes a crisis. "It's amazing to me how anyone can get a kick out of destroying that much property," Suffia said.