British and US firms were infected with a computer virus this weekend that arrives via e-mail and convincingly masquerades as an innocent plain text file.
The bug, called 'Stages.worm', does not damage computer files but can shut down corporate e-mail servers.
While there is some concern that employees arriving on Monday morning may be fooled into opening e-mail that carries the bug, anti-virus companies say that a wide-scale outbreak is not expected.
"We're going to find out on Monday," said Dan Shrader, spokesperson for anti-virus firm Trend Micro. He said two large aerospace companies were hit with the virus on Friday afternoon, and one of the largest companies in the country was infected on Saturday. Still, he said, "as of Friday (it) didn't look like it was going to be a huge situation."
The virus is particularly tricky because it utilizes a rare file format called 'windows scrap files'."= The extension for this file type, which should be '.shs', never appears.
That means it's easy to make a scrap file appear to be another file type; Stages.worm arrives ending with the letters '.txt' suggesting that it's a text file.
Internet users are advised not to open attachments they did not expect to receive, no matter what the file extension may appear to be.
"If you didn't expect it, you should check with the sender before you open any attachment, no matter what the extension is," said Mary Landesman, spokesperson for anti-virus firm Command Software Systems.
The virus was apparently authored by a familiar Argentinian virus writer named 'Zulu' and was released 26 May. But the first infections were not found until Friday.
"I don't see anything indicating a widespread release," Landesman said. Her firm had found only four infected companies by Sunday. "But that doesn't mean it's not sitting in a lot of people's inboxes. ... It is a holiday weekend."
'Stages.worm' spreads like the Melissa virus and the Love Bug, sending copies of itself to e-mails listed in the victim's Microsoft Outlook address book. But the virus sends out a maximum of 100 copies each time. It arrives with one of several randomly chosen subject lines. One sample has in the subject line 'Funny'; the body of the message reads, 'The male and female stages of life', and the attachment is named 'Life_Stages.txt'."= Other possible subject lines are: 'life_stages', 'jokes' and 'text'.
After infection, the worm does display humorous text:
The male stages of life: Age. Seduction lines. 17 My parents are away for the weekend. 25 My girlfriend is away for the weekend. 35 My fiancee is away for the weekend. 48 My wife is away for the weekend. 66 My second wife is dead.
Age. Favourite sport. 17 Sex. 25 Sex. 35 Sex. 48 Sex. 66 Napping.
Age. Definiton of a successful date. 17 Tongue. 25 Breakfast. 35 She didn't set back my therapy. 48 I didn't have to meet her kids. 66 Got home alive.
The female stages of life:
Age. Favourite fantasy. 17 Tall, dark and handsome. 25 Tall, dark and handsome with money. 35 Tall, dark and handsome with money and a brain. 48 A man with hair. 66 A man.
Age. Ideal date. 17 He offers to pay. 25 He pays. 35 He cooks breakfast next morning. 48 He cooks breakfast next morning for the kids. 66 He can chew his breakfast.
Take me to the Virus Workshop