Lawrence Livermore National Laboratory and other research institutions and corporations were scrambling today to protect themselves against an anticipated wave of invading hackers armed with a dangerous new tool. SATAN, a piece of computer software designed to help companiesplug leaks in computer security, was released on the Internet today amid widespread fears that it could help malicious hackers do just the opposite. Designer Dan Farmer was fired by Silicon Graphics when he decided to release the easy-to-use program -- Security Administrators Tool for Analyzing Networks. Farmer maintains that releasing the software would force organizations to take better security precautions. TIME technology writer Joshua Quittner predicts that SATAN will become "the Michelangelo of 1995," referring to the hyped virus program that scared computer operaters three years ago, but never showed up.