According to anti-virus company Symantec, the worm, known as "SirCam", is different to the usual Trojan in that it randomly attaches itself to a document in the users Microsoft Office directory and sends it on to everyone in the address book.
The subject line of the email is the name of the file the worm attached itself to.
"There is a certain amount of privacy issues associated with it, it's not good if you've got a document about someone's performance and it gets sent around," a spokesperson for Symantec told ZDNet.
Originating in South America, the virus has turned up in the United States, with a few reports of infection. It has not been detected in the Asia-Pacific region.
Symantec has the virus currently rated as a medium risk.
"It's not a new technique, but we don't see it very often," the spokesperson said.