A recent Cambridge University study, photos deleted from photo sharing sites such as Facebook were still available thirty days later.

According to the BBC, sites like Facebook store photos in one place and their main page in another, which can account for a delay from the time that you delete a photo to actual photo deletion. Seven of the sixteen sites tested, including Facebook, failed the test.

Facebook allegedly denies the findings of the study, telling CNN.com that “when a user deletes a photo from Facebook, it is removed from our servers immediately.”

Whether the findings of the study are accurate or not, studies like these serve as a warning to anyone who posts photos online—make sure that you aren’t posting anything that would embarrass you if your co-workers, clients, relatives, friends, or potential employers saw it.