Washington, Tues. - A new computer virus, which looks like a harmless text file, has caused shutdowns of the e-mail systems at four Fortune 100 companies, antivirus experts said yesterday. The virus does no harm to computer files.

While users are well-warned about VisualBasic attachments, which appear as ".vbs" extensions, the so called "Stages" virus looks like a text file, complete with ".txt" extension. But the real extension is ".shs," which stands for Windows Shell Scrap Object.

A scrap file can contain anything, including executable and malicious code. The ".shs" extension does not appear even if a user sets Windows to show all file extensions.

The virus hit companies in the US by Friday and began appearing in Asia over the weekend. -AP