New updates fix a potentially disastrous flaw.
Several personal firewall vendors have released updates addressing your vulnerability to intruders who get in when you unsuspectingly run a malicious application that masquerades as a friendly one. The problem garnered public attention thanks to PC security guru Steve Gibson, whose Gibson Research Web site is best known for ShieldsUp, a test designed to expose a firewall's vulnerability to external attacks. Antivirus software can alert you to known Trojan horses, but if a new one gets through, your firewall is supposed to provide a second line of defense. Unfortunately, most personal firewalls failed LeakTest when it was released in December. All firewalls are meant to block unauthorized attempts to access a PC from the outside.