The CIA is conducting a cyber-war game this week geared to simulate a major Internet attack by enemy computer hackers, an intelligence official said Thursday. Dubbed Silent Horizon," the three-day unclassified exercise is based on a scenario set five years in the future and involves participants from government and the private sector. Online crime has exploded in recent years, a result of organized crime groups based in Eastern Europe. But investigators so far have uncovered few links to Islamic extremists.