Leaked copies of Windows 7 hit the Internet only hours after Microsoft Corp. handed out a preview build to developers last week, according to searches at several BitTorrent-tracking sites.

The notorious Pirate Bay site, for example, first noted the 32-bit version of the upcoming operating system on Oct. 29, just one day after Microsoft unveiled Windows 7 to attendees at its Professional Developers Conference in Los Angeles. A 64-bit edition was posted the following day.

As of midday Sunday, with several copies of Windows 7 available, downloading was brisk. One 32-bit torrent listed on Pirate Bay showed more than 1,400 "seeders," the term for a computer that has a complete copy of the torrent file, and close to 5,300 "leechers," or computers that have downloaded only part of the complete torrent. The 32-bit torrent installs a copy of Windows 7 Ultimate, according to users commenting on the site.

Traffic on the 64-bit edition was lighter: Pirate Bay's longest-available torrent showed about 260 seeders and approximately 900 leechers.

BitTorrent sites such as Pirate Bay, Mininova and Seedpeer all listed the 32-bit version of Windows 7 as weighing in at 2.72GB, while the 64-bit edition was tagged as 3.36GB.

Microsoft talked up Windows 7 for the first time in detail last Tuesday, when Steven Sinofsky, who heads Windows development, and other company executives, presented the new operating system in a keynote address and multiple technical sessions. Developers, as well as some reviewers and bloggers, were given what Microsoft dubbed "pre-beta" copies of Windows 7 later that day.

The company has watched its operating systems repeatedly leak to BitTorrent sites. In mid-2007, for instance, several builds of Windows Vista Service Pack 1 (SP1) that had been given to an invite-only group of some 15,000 testers ended up on BitTorrent within days. Last February, the final version of Vista SP1 made it to the Web weeks before paying customers were allowed to download the update. Several months later, Windows XP SP3 was available on Pirate Bay before it was officially released to users.

Microsoft isn't the only operating system maker whose code has leaked, however. In June 2007, a beta of Apple Inc.'s Mac OS X 10.5, a.k.a. "Leopard," was posted to BitTorrent sites. Unlike three years before, however, when Apple sued 28 people, most identified only as "Does," for releasing a developer preview of Mac OS X 10.4, the company took no legal action to stop the leaks.

Windows 7 is slated to enter a public round of beta testing sometime early in 2009, according to statements made last week by company officials.