Users who have already downloaded the leaked copies of Windows 7 Release Candidate (RC) on file-sharing sites complain that the upgrade contains malware. Windows 7 RC will officially be launched by Microsoft Corp. this week, but pirated copies appeared two weeks ago, firstly on BitTorrent tracking sites on April 24. Some of the pirated builds include a Trojan horse, numerous users said in message forums and in comments on BitTorrent sites such as Mininova.org.Microsoft, which has cited potential infection as a reason to steer clear of unauthorized downloads, jumped on the news. Alex Kochis, director of Microsoft's Genuine Windows anti-piracy technology group, said in a post to a company blog on Friday: "This unfortunately shows that there are those out there who see the significant interest in something such as Windows 7 as an opportunity to try to take advantage of others.” Windows 7 RC is not the first leaked software found to harbor attack code. For example, in January 2009 security experts warned that pirated copies of Apple Inc.'s then-new iWork '09 suite contained a Trojan horse that hijacked Macs. Microsoft will let the general public download Windows 7 RC on Tuesday, but has not fixed an exact time it will make the upgrade available. Subscribers to TechNet and the Microsoft Developers Network (MSDN) have been allowed to download the RC since last Thursday.