(security) staying logged into any website for longer than needed...

...yet another reason why that is bad.

http://www.infoworld.com/article/08/08/01/A_photo_that_can_steal_your_online_credentials_1.html

Quote: There is one catch, however. The victim would have to be logged into the Web site that is hosting the image for the attack to work. "The attack is going to work best wherever you leave yourself logged in for long periods of time," Heasman said.