Internet service provider Comcast is warning users to clean up their PCs or face having their web connection cut off.

The US firm’s ultimatum follows a similar decision by Scandinavian ISP TeliaSonera, which sent warning letters to customers exploited by spammers.

Spammers were reported to have used customers’ PCs as ‘zombies’, which acted as a spam distributor.

Comcast warned customers to keep their PCs clean after some of its IP addresses were discovered on anti-spam blacklists, which stopped some users sending emails.