Attackers have found another hole in Microsoft's Office products. On Thursday, Symantec reported that it has discovered a targeted attack that takes advantage of an unpatched vulnerability in Microsoft's PowerPoint software.

The hackers behind this attack are using the same techniques that were used in previously reported Word and Excel attacks, said Dave Cole, director at Symantec Security Response. "It's similar to the pattern we've seen over the past few months where they're using a previously unknown Microsoft vulnerability and an email enticement to get a backdoor to someone's machine."

Cole believes the same hackers may be behind all three attacks. "It looks like it may be the same group, based on the similarity of the attacks," he said.

As with the Word and Excel incidents, this latest malware is not widespread.

This PowerPoint attack was discovered late on Wednesday by a Symantec customer, who received a Chinese-character email from a Gmail account. The email contained a PowerPoint attachment that installed two pieces of malicious code when opened: a Trojan program, called Trojan.PPDDropper.B, and a backdoor program called Backdoor.Bifrose.E.

The backdoor program tries to cover its tracks by writing over the original PowerPoint document. It then awaits instructions from the attackers, who can use it to control the infected system.

Office is fast becoming the target of choice for hackers.

Microsoft patched a total of 12 Office vulnerabilities on Tuesday, but the PowerPoint bug used by this latest malware was not one of them, according to Cole.

Microsoft is investigating the vulnerability, said Stephen Toulouse, a security program manager with Microsoft's security response centre.

Symantec is studying it as well. The security vendor said it does not yet know if the attack is specific to PowerPoint, or whether it affects all Office products.