Washington, July 22 - Beware, emails or Facebook posts or pictures can resurface months after they are deleted -- in the wrong hands or at the wrong time, according to researchers.

'If you care about privacy, the internet today is a very scary place,' said University of Washington (UW) computer scientist Tadayoshi Kohno. 'If people understood the implications of where and how their email is stored, they might be more careful or not use it as often.'

For instance, a lost cell phone can expose personal photos or text messages. A legal investigation can subpoena the entire contents of a home or work computer, uncovering incriminating, inconvenient or just embarrassing details from the past.

The team of UW computer scientists developed a prototype system called Vanish that can place a time limit on text uploaded to any web service through a web browser. After a set time text written using Vanish will, in essence, self-destruct.

Study co-authors include Roxana Geambasu, Tadayoshi Kohno, Hank Levy and Amit Levy, all with UW's department of computer science and engineering.

'When you send out a sensitive email to a few friends you have no idea where that email is going to end up,' Geambasu said.

'For instance, your friend could lose her laptop or cell phone, her data could be exposed by a hacker, or a subpoena could require your e-mail service to reveal your messages.