SAN FRANCISCO, FEBRUARY 12: The US investigators tracking hackers who shut down top Web sites turned their focus to the sites used to launch the attacks on Friday as President Bill Clinton called a summit on Internet security for next week.The Federal Bureau of Investigation was backtracking through sites that were penetrated and used as "zombies" to hit others. The agency, at a briefing this week, underscored the importance of "unwitting third parties" used to conceal themselves by launching massive co-ordinated attacks on the top E-commerce sites.The University of California-Santa Barbara said that its computer system was used to aim an attack at the CNN Web site brought down in the week's wave of Internet sabotage, a spokesman said Friday. The university said it was providing details to the FBI for the investigation.`ZOMBIE' ATTACKER FOUND: In Palo Alto, meanwhile, computer security company Network Associates Inc said it had located another one of the "zombies" used to launch the attacks a computer in Germany which has since been disconnected from the Internet.But while the university and the security firm stepped forward, computer experts said scores more remained silent, fearing legal action or involvement in costly criminal probes. "People want to stay out of the way," said Stuart McClure, president of the Irvine, California-based Ramparts Security Group. "People are really sensitive about these issues they think the perception would be negative."Perceptions of Internet security took another hit on Friday when a small California Internet company said an unrelated hacker attack on its system this week had apparently gained access to consumer credit card numbers.RealNames, a San Carlos, California, business, said the extent of the damage was hard to assess because the attack had come through mainland China, and the connection appeared to have shut down while the hackers were downloading data. "Our best guess is that this was done by a traditional hacker, whose goal is not to steal but to prove that he has the ability to steal," said Real Names CEO Keith Teare, whose company sells a simplified Internet address system to about 50,000 customers.In Washington, Clinton's summit is expected to boost broader co-operation in a young industry that's growing fast and hasn't made security a high priority. The industry, in turn, wants to give advice to federal regulators seen as too unsophisticated in Web ways to have much impact. Clinton warned not to expect Tuesday's meeting to come up with an "instantaneous solution" to a wave of hacking attacks which this week took down popular sites Yahoo!, leading retailers Buy.com, eBay, Amazon.com and the news site CNN.com.While computer security has often vexed individual computer users linked to the Internet, major Web sites have been hit only by sporadic outages, and nothing like the chaos of the past week.BROADER COOPERATION: The UC-Santa Barbara report was one of the first to indicate that the hackers' tracks were slowly being uncovered.