There's a saying that if you want to keep something private, keep it off the internet. No matter how many safety measures you take, stuff has a tendency to leak out once you hand it off to someone else's care.
Case in point is a Flickr bug that set the private photos of some users to public.
The bug only affected a few people, Flickr says, but it stayed undetected for 20 days, during which time all the photos were available to anyone, anyone who knew where to look at least.
While the photos were made public, you still had to know their URL to get to them, they did not show up in search results. However, Flickr can't tell those affected if their photos were actually viewed by someone else or not.
For now, Flickr has contacted those involved and set all of their photos to private. People, understandably, aren't thrilled by all of this.