There are lots and lots of blogs and forums who talk about leaked copies of Windows 7, however we advise you to beware of those downloads, since many of those installation could be spiced up with a variety of worms, viruses and spywares, that may compromise your privacy and security.
However if you have downloaded a copy of Windows 7, before you go ahead and install it, a small tool called Windows 7 ISO verifier can save you a lot of trouble.
Once you have downloaded a copy of Windows 7, before you install it, just use this tool to verify the downloaded file, if the file is valid you should see a message saying so.
However if you see a different message it would certainly mean that the installation is gamed to install spywares, malwares, viruses or Trojans, just delete it and wait for Microsoft to release a official version. Thanks Nirmal.