The worm targets Windows computers that run specific security firewalls. A quickly spreading Internet worm destroyed or damaged tens of thousands of personal computers worldwide Saturday morning by exploiting a security flaw in a firewall program designed to protect PCs from online threats, computer experts said. The “Witty” worm writes random data onto the hard drives of computers equipped with the Black Ice and Real Secure Internet firewall products, causing the drives to fail and making it impossible to restart the PCs. Unlike many recent worms that arrive as e-mail attachments, it spreads automatically to vulnerable computers without any action on the part of the user. At least 50,000 computers have been infected so far, according to Reston, Va.-based computer security firm iDefense and the Bethesda, Md.-based SANS Institute. Full Story