Computer worms that have brought down systems around the world in recent days are starting to attack each other, Finnish software security firm F-Secure said on Wednesday. "We seem to have a botwar on our hands," said Mikko Hypponen, chief research officer at F-Secure. "There appear to be three different virus-writing gangs turning out new worms at an alarming rate, as if they were competing to build the biggest network of infected machines."Hypponen said in a statement that varieties of three worms -- "Zotob," "Bozori" and "IRCbot" -- were still exploiting a gap in Microsoft Corp.'s Windows 2000 operating system on computers that had not had the flaw repaired and were not shielded by firewalls. "The latest variants of Bozori even remove competing viruses like Zotob from the infected machines," Hypponen said in a statement on the company's Web site. (http://www.f-secure.com) The worms were blamed for major system trouble at some media outlets and companies in the United States on Tuesday, causing personal computers to restart repeatedly and potentially making them vulnerable to attack. Microsoft and the top computer security companies, Symantec Corp. and McAfee Inc., said damage to systems on Tuesday had been limited and was unlikely to cause widespread havoc like that which resulted from other malicious software such as "SQL Slammer" and "MyDoom."