O2 has suspended its web-based picture message (MMS) viewing service after photos sent privately to others were found online.

The problem, discovered by anti-spam blog Mail Channels, has affected users of handsets that can't display picture messages, such as Apple's iPhone.

Rather than seeing the message, users of these handsets receive a text message with a link to a web-based viewer. However, as no username or password is required to view the message, Mail Channels found that some images could be viewed through a simple Google search.

According to Mail Channels, the images were displayed with the sender's phone number.

David Cawley, a representative for the blog, said: “As these web pages were wide open to the internet, not requiring any authentication, a very small handful were indexed by Google.”

O2 has suspended the website viewing service. A representative for the network provider told us: "We have temporarily taken down our MMS web-based viewing service while we investigate this issue fully.”

He added that users with MMS-enabled handsets were not affected by the issue.