The moderators have announced that copies of Microsoft products, including Windows are no longer allowed on /r/softwareswap.

There has been some speculation on /r/pcmasterrace over the past few days, but now it's official.

To quote:

I was contacted about 3 days about by a member of the staff here on reddit (one of the site admins), who informed me of some legal issues reddit was facing due to the keys sold on this subreddit. I was presented with two choices, either quickly and quietly clean up this subreddit of all seller threads and ban the sale of the keys, or let the subreddit be closed by the admins.

...

For now, the sale of any and all Microsoft products has been banned from this subreddit.

I personally bought a Windows 8.1 Pro key and found it to be blocked later. Some other users have found the same thing to happen.

For more information, there's a sticky post on /r/softwareswap now.