C:\1

Hi geeks, I recently bought a new game and went to install it, but an error came up saying not enough space. I always have my partitions setup with a 40gig OS (C:) and the rest as Data (D:). I rarely have more than 15gig in my C: , usually about the 10gig mark, so I should have had heaps of space. After scanning for malware, cleaning up my hard disk and defragging, I opened C: and there was a folder called 1. I had never seen it before, it hadn't been there the last time I checked (few days max). I right-clicked, properties, and it says 29.5gigs used. I thought "weird", so I opened it and it was full of extension-less files, counting from 1 and ending at 8000+ before going through the alphabet also a few times. As they had no extensions and I hadn't put them there, I just deleted the folder and re-scanned and defragged before installing my game, which worked fine.

So the question is: What was that folder? What were the files inside? I can't find anything like it on an internet search, but I don't really know how to describe it to the search engines. Everything I did try just brought back weird and different results. The computer is still kicking hard, it's running really quick - always was before this, and is now.

Any ideas?