Hackers have been sending malicious PDF files to U.S. military contractors, posing as messages from the U.S. Department of Defense.

"Opening the malicious PDF file attached to the spoofed emails triggers an attempt to exploit an Adobe Reader vulnerability only patched by the software firm last Tuesday (12 January)," writes The Register's John Leyden.

"The infection of vulnerable systems opens up a backdoor that connects to a server hosted in Taiwan, though the hackers who set up the attack may potentially be located anywhere," Leyden writes.

Click here to read the story at The Register.