TechCrunch:

When does “delete” really mean delete? Not always, or even at all, if you’re Twitter.

Twitter retains direct messages for years, including messages you and others have deleted, but also data sent to and from accounts that have been deactivated and suspended, according to security researcher Karan Saini.

Brings to mind the old cliche of “Don’t write down anything you don’t want your mother to read.”