Undead deleted photos linger on social networking websites

That embarrassing party shot of you and that hot dog may still come back to haunt you - photos posted on social networking websites can often be easily viewed even after users attempt to delete them, according to a study by security researchers at the University of Cambridge.

Researchers posted photos on 16 social networking and Web 2.0 websites, keeping a careful record of the URL associated with the photos, before deleting the images. Even after this supposed deletion the researchers were able to find the photos on seven of the 16 websites a month later, simply by visiting the web location associated with the image.

The problem arises because sites often fail to remove image files from their photo servers after they are deleted from the main website.

Photo-sharing sites such as Flickr and Google's Picasa, as well as Microsoft's Windows Live Spaces, removed content from its servers upon deletion. But photos posted on sites including Facebook lingered in caches, even after images were removed from a user's profile. Other offenders include MySpace and Bebo.

A summary of the study - entitled Attack of the Zombie Photos - can be found here.

Joseph Bonneau, one of the PhD students involved in the study, criticised a "lazy approach" to user privacy by some social networking websites, which could be in violation of data protection rules banning the retention of personally-identifiable data for longer than necessary.

However, a spokesman for Facebook said that the site does delete photos from its systems once users remove them from their profile, claiming that images were only available because they were cached elsewhere.

A Facebook spokesman told the BBC: "URLs to photographs may continue to exist on the Content Delivery Network (CDN) after users delete them from Facebook, until they are overwritten. Overwriting usually happens after a short period of time."

The issue, much like the easy availability of supposedly deleted posts to micro-blogging website Twitter, serves as a further wakeup call to Web 2.0 fans that information posted onto social networking sites often isn't removed by simply deleting it. ®