
The devices 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 prize is connected to a computer. We therefore recommend consumers not to use the prize," the company said on its website.
The chain has released software that removes the malware from infected systems.
The contest ran during of August and the prizes were shipped out late September. Contestants had to peel a sticker of a drink, revealing a unique code that they then entered on the McDonalds website.