KezNews.com posted information about, and a tool for, cranking out legitimate Windows Vista activation keys. But even though the tool churns through 20,000 keys an hour, it could take billions -- maybe trillions -- of years to work through all the possible combinations.

Microsoft said it is investigating the attack. "We're looking into this issue now," said Alex Kochis, senior product manager of WGA (Windows Genuine Advantage) , on the group's blog.

According to the KezNews.com write-up by someone identified as Computer User, who created the "KeyGen" tool, the process uses a modified version of the software license manager script file to search for valid keys. Crackers, however, must periodically check to see if the key they entered earlier has changed, then attempt to activate using the changed key. Those parts of the procedure can only be done manually.

Vista's activation, which is part of the company's overall anti-counterfeit program, validates the license's product key -- in Vista's case, that's a 25-character alphanumeric string -- to make sure that the key isn't used multiple times by pirates. If Vista is not activated within 30 days of its first-time use, it drops into a crippled state in which only the browser works, and then only for an hour at a time.

Computer User claimed that KeyGen can check about 20,000 keys an hour, but warned others that it could take "hours, days" to come up with a working activation key. One wag on the KezNews forum did the math and concluded that it would take 1.35 quintillion years -- that's 1,351,869,740,791,670,000 years to be exact -- for the tool to work its way through all of the possible key combinations.