The US Computer Emergency Response Team (Cert) at Carnegie Mellon has issued an alert over spam emails claiming to come from the US Department of Justice (DoJ).

Similar to a set of spam sent out in June, the email warns that a complaint has been made against the recipient.

"These messages contain a malicious attachment that supposedly contains information regarding complaints filed against the recipient's company with the DoJ," said the latest Cert bulletin.

"The attachment launches malware on the user's system when opened."

The attachment is a Trojan downloader that copies itself onto the computer's registry files and reports back to the sender for further instructions.

The attacks started last night, according to web filtering firm Websense, and were initially targeted at finance houses in the US, western Europe and the Pacific Rim.

The quality of the spam messages is higher than usually found in such attacks. The email address has been spoofed to simulate 'complaintscentre@usdoj.gov' and graphics from the actual website are included.