[FMX] How to perform a "destructor" like action when browser window is closed

I have a chat program built using flash for the front end tied to a J2EE back end. My program creates socket connections which must be closed appropriately when a user signs off.

When a user decides to sign off they can click the sign off button and everything is peachy. However, a less responsible user may choose to sign off by simply killing the browser window. Is there any way to implicitly call an actionscript routine on this event?