NEW YORK: A new computer virus spreading across the Internet is infecting machines by e-mail like the recent Melissa virus- -but causing more damage by ruining computer files.

Anti-virus teams in the government and at universities were trying on Thursday to determine the severity of the outbreak of "Worm.Explore.Zip," a virus that arrives by e-mail with an attached file that can infect a computer. Numerous software companies issued warnings about the virus.

It wasn't immediately clear how many machines or networks had been stricken.

General Electric temporarily shut down its e-mail system when the virus was detected, but damage was minimal because computer personnel were on the lookout for the bug. Microsoft cut off its corporate e-mail connection with the Internet for two hours as a precaution.

At least one smaller business didn't fare so well.

"We have the virus," said Rachel Albert, a spokeswoman at InterActive Public Relations of San Francisco. "It's terrible. A lot of people lost everything they were working on."

Virus experts said the number of calls reporting problems was substantially higher than normal. Some Web sites took their e-mail systems off line to slow the spread of infection, said Shawn Hernan of the Computer Emergency Response Team at Carnegie Mellon University in Pittsburgh.

Trend Micro, a maker of anti-virus software, said five large customers reported on Thursday that their systems were infected.

Worm.Explore.Zip arrives by e-mail with a friendly message: "Hi (Recipient Name)! I received your email and I shall send you a reply ASAP. Till then, take a look at the attached zipped docs."

The virus actually isn't dangerous unless the computer user opens the "zipped docs," a term referring to a compressed file sent along with the e-mail. By opening that file, a computer user inadvertently activates the virus.

The virus then worms its way into the computer user's e -mail program and sends a copy of itself to the address of any e-mail that subsequently arrives.

It also hunts through a computer's hard drive and deletes the information in files created by popular software programs, including Microsoft Word and Microsoft Excel.

Anyone who receives the e-mail message or e-mail with an attachment shouldn't open it, said Mark Zajicek of the Computer Emergency Response Team.

"Don't click on it, don't run it, don't execute it," he said.

The virus is the third to draw national attention since late March, when the Melissa virus overwhelmed computer networks with floods of e-mail. Melissa did not destroy files, however.

A more damaging virus named Chernobyl struck in late April.