Microsoft is developing a patch for a newly discovered security flaw in versions of Windows XP which poses a particular threat to computers running XP Media Center edition.

The flaw is in Windows Remote Desktop Services (RDS) and could allow a hacker to cause a computer to crash repeatedly by sending specially crafted data packets.

Although all versions of XP have RDS, it is only turned on as standard in Media Center edition.

"Our investigation has determined that this is limited to a denial of service attack, so an attacker could not use this vulnerability to take complete control of a system," said Microsoft in a security advisory.

"Services that use the Remote Desktop Protocol are not enabled by default, but if a service were enabled an attacker could cause this system to restart."

Microsoft said that it will release a patch as soon as possible and is " aggressively investigating" reports of the flaw.

The user who discovered the vulnerability, security researcher Tom Ferris (aka 'badpack3t'), claims that he alerted Microsoft to the problem in May. The company told him that a patch would be released on 9 August as part of the usual monthly cycle. 

"I have been working with Microsoft to get a patch out for this," said Ferris. "Microsoft told me the patch was going to be released in August. We know it's only a DoS [denial of service attack], which is kind of boring, so this is why we decided to report it to Microsoft."