Somebody's been uploading RPG materials to the Internet Archive:
Some of this is blatantly illegal. Other stuff is from folks's blogs or is Creative Commons licensed (like all of the One Page Dungeon compilations).
If you've posted a free PDF of your stuff online, you might want to check to see if you've been included. There are lots of older fanzines that have been culled from my zine list (I found an archive chat log that specifically mentions this, here), but a lot of other material is from people's blogs--like all of Gus's stuff from Dungeon of Signs.
I don't know what recourse you have if you don't want your stuff included in the Internet Archive.