A Trojan horse is circulating in spam emails claiming to come from the Better Business Bureau. 

The email warns that legal action is being pursued against the recipient, but the attached file contains malware that attempts to install a key-logger.

"Attached to the message is a Word document (Document_for_Case.doc) supposedly containing additional details regarding the complaint," said internet monitoring company Websense.

"The document actually contains a Trojan that attempts to download and install a key-logger which uploads stolen data to an IP address in Malaysia."

Email users are being warned to be on their guard and to update antivirus signature files immediately.