[Update] This issue has, of course, affected users of the Spotify free service, which is advertisement supported.
Digital music service Spotify has reported that it has turned off third party display ads until further notice, due to some of their customers reporting malware infections after visiting the site. This is thought to have been caused by a third party advertisement on the Spotify service, and engineers at Spotify are trying to find out which advertisement.
Techcrunch and The Register (who broke the story) have all put out content covering this, so it should be taken as a serious threat, and we strongly advice ensuring users have a fully up-to-date antivirus and anti-spyware solution in place on their systems in order to protect them.
As we reported here, this type of security threat is seeing growth in the wild, and exceptional care must be taken by users when visiting any site that displays third-party services advertising, which alas, covers most sites; this is fast becoming the new hot infection vector.