Last Wednesday, on February 24th, Black Mesa developer Joe "Fr0z3n" Radak posted an alert describing a security vulnerability for games running on the Source engine[forums.blackmesasource.com], albeit one that only users who frequent multiplayer games running on the engine should be concerned over. For more information, click the link.

Be careful when joining servers for Source games!

EDIT: Replaced my subpar attempt at journalism with something more practical.