President Clinton says the attacks that shut down some web sites temporarily last week showed the need for greater security, but was not “Pearl Harbor.” An Iowa State Univesity computer science professor says the attacks could be just the beginning. Doug Jacobsen says the messages sent by the attackers aren’t easy to block.Jacobsen and a collegue run a systems security laboratory which does research on hackers. He says any computer with high-speed internet access could potentially be used by the hackers.He says universities are not immune from hacker attacks.Jacobsen says the university is doing its best to prevent hackers from using the university computers. He says they’re also working to prevent any attacks on the university system.