The antivirus-killer Bugbear has mutated into Bugbear.B and is on the loose, according to security experts Antivirus companies warned PC users on Thursday that a variant of the nine-month-old Bugbear virus has started spreading across the Internet, installing tools on infected computers that let intruders control the systems. Security-software company Network Associates graded the virus a medium-level threat on Thursday morning, but three hours later it upgraded that to high. “It has gone to the No. 1 (threat) for the day in about 12 hours,” said Jimmy Kuo, an antivirus research fellow with Network Associates. The virus, called Bugbear.B, is very similar to the original Bugbear program released last September. The virus spreads by selecting an email in the victim’s in-box and attaching itself to a reply to that message, which it then sends out to any email addresses that it culls from the user’s system. The virus will also occasionally create its own messages using various subject lines. Full Story