By REUTERS - Microsoft Corp. on Wednesday offered a $500,000 reward for information leading to the arrest of the authors of the crippling MSBlast and Sobig computer bugs. Microsoft offered $250,000 apiece for the writers of the viruses, two of the costliest computer-bug outbreaks to hit the Internet. The bugs wreaked havoc across the world in August and September, attacking computers that run on Microsoft's Windows operating system. "These are not just Internet crimes, cyber crime or virtual crimes. These are real crimes that hurt a lot of people,'' Microsoft General Counsel Brad Smith said in a statement ahead of a news conference in Washington. Microsoft officials were joined by U.S. and international law-enforcement groups as they announced the rewards at the press conference. Security experts familiar with the continuing cyber dragnet said the trail had recently run cold. The unprecedented lure of cash was seen as a way to generate new leads, sources said. "Apparently, they haven't had too much luck, which is why they are resorting to offering money, which could work for Blaster,'' said Mikko Hypponnen, research manager at Finnish anti-virus firm F-Secure. Blaster, also known as MSBlast or LovSan, triggered a torrent of data traffic across the Internet, bogging down corporate networks and knocking some machines offline. Theories abound that the author wrote the worm to impress a girl, possibly named "San'' -- short for Sandy. "I could see a teenager snitching on that one. SoBig is a different story. I think that's the work of an organization or group,'' Hypponnen said. Sobig infected hundreds of thousands of PCs around the globe, installing a program on some machines that could allow it to be controlled by outsiders to send spam e-mails. Because of the spamming connection, law enforcement officers and security experts suspect the Sobig authors wrote the malicious code for profit motives, stoking fears that organized groups may increasingly resort to this form of cyber-sabotage in the future.