Microsoft has acknowledged a glitch with its Windows XP Service Pack 1 update that can cause system slowdowns.

The company has confirmed that after installation of SP1 some programs may take as much as 10 times longer to start.

The glitch came about because of changes made in SP1 to Windows XP's memory management system. It only affects programs that allocate and re-allocate large chunks of memory.

But although Microsoft has developed a fix for the problem it is not yet widely available. Currently the only way to obtain it is to contact the company's Product Support Services department, as additional testing may need to be carried out.

Microsoft recommends waiting for the next service pack to be released to fix the glitch.