Fast food chain McDonald's has recalled 10,000 MP3 players handed out as prizes in a contest in Japan, after discovering that the devices were infested with malware. 

The players came bundled with 10 songs, as well as a variant of the QQPass Trojan which is configured to steal user passwords. 

"The virus poses an infection risk when the MP3 player is connected to a computer. We therefore recommend consumers not to use the prize," the company said on its website.

McDonald's has released software that removes the malware from infected systems.

The contest ran during August and the prizes were shipped out in late September. Contestants had to peel a sticker off a drink, revealing a unique code which they then entered on the McDonald's website to see whether they had won.