A new virus that hijacks PCs via the popular PowerPoint program is on the loose according to Microsoft.

The virus contains a booby-trapped presentation that, if opened, installs keylogging software on to the users PC.

Microsoft are urging Windows users to be on their guard because it could be weeks before a patch is produced to combat the security loophole.

Up to now relatively few people are thought to have fallen prey of the poisoned presentation.

The weakness that the malicious hackers responsible for the virus have exploited has been found in PowePoint 2000, 2002 and 2003.

Security specialists claim the virus was aimed at businesses in Asia because Chinese characters are used in the subject line of the email the poisoned files are attached to and in the name of the booby-trapped PowerPoint presentation.

The presentation claims to be 18 comical slides about relationships between men and women.

Any person opening the PowerPoint file will activate the virus that installs a keylogger that records everything typed on an infected computer. It also enables the hackers to get inside the machine and install other malicious programmes.

As soon as a computer has been tainted with the virus, a blank version of the poisoned presentation is installed that covers up the infection.

The virus has been dubbed as a "zero-day" attack as there is no known defense against it at the current time.

To protect themselves against hackers exploiting the bug, Microsoft warned users not to open or save PowerPoint files that turn up unexpectedly - even if they are from trusted sources.

The virus containing the booby-trapped PowerPoint files started circulating a day after Microsoft issued a series of software patches as part of its regular security updates. Typically these updates are issued on the second Tuesday of every month.

Security firms said the timing was deliberate as it gave the virus the longest chance to rack up victims before Microsoft gets round to closing the loophole.

Microsoft said it was on target to release a patch to protect against the exploit on 8 August