*No such thing as "deleted" on the Internet*

Thu May 21, 2009 11:51AM EDT

It's always fun to write about research that you can actually try out
for yourself.

Try this: Take a photo and upload it to Facebook, then after a day or
so, note what the URL to the picture is (the actual photo, not the page
on which the photo resides), and then delete it. Come back a month later
and see if the link works. Chances are: It will.

Facebook isn't alone here. Researchers at Cambridge University (so you
know this is legit, people!) have found that nearly half of the social
networking sites don't immediately delete pictures
<http://news.bbc.co.uk/2/hi/uk_news/8060407.stm> when a user requests
they be removed. In general, photo-centric websites like Flickr were
found to be better at quickly removing deleted photos upon request.

Why do "deleted" photos stick around so long? The problem relates to the
way data is stored on large websites: While your personal computer only
keeps one copy of a file, large-scale services like Facebook rely on
what are called content delivery networks to manage data and
distribution. It's a complex system wherein data is copied to multiple
intermediate devices, usually to speed up access to files when millions
of people are trying to access the service simultaneously. (Yahoo! Tech
is served by dozens of servers, for example.) But because changes aren't
reflected across the CDN immediately, ghost copies of files tend to
linger for days or weeks.

In the case of Facebook, the company says data may hang around until the
URL in question is reused, which is usually "after a short period of
time." Though obviously that time can vary considerably.

Of course, once a photo escapes from the walled garden of a social
network like Facebook, the chances of deleting it permanently fall even
further. Google's caching system is remarkably efficient at archiving
copies of web content, long after it's removed from the web. Anyone
who's ever used Google Image Search can likely tell you a story about
clicking on a thumbnail image, only to find that the image has been
deleted from the website in question -- yet the thumbnail remains on
Google for months. And then there are services like the Wayback Machine,
<http://www.archive.org/index.php>which copy entire websites for
posterity, archiving data and pictures forever.

The lesson: Those drunken party photos you don't want people to see?
Simply don't upload them to the web, ever, because trying to delete them
after you sober up is a tough proposition.



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