After probing Steams code some people found detail within Steam that lead them to think that Steam watches what's on your hard drive....
Valve's main man, Gabe Newell says,
"Not true. We have no interest in what's on your hard drive.
When we first heard about this, we were perplexed. Then we realized that
the people who were seeing this were running FAT32 instead of NTFS. In
Windows, if you have the NTFS file system, it zeros out sectors before it
reallocates them. With FAT32, it doesn't. So if you allocate a large file
(it doesn't matter if it's a Steam cache or some other application's files),
in FAT32 if you open that file, you will see whatever data was left over
from the previous writes to those sectors until your application writes over
that data with new data. So on FAT32, Steam allocates 400 MB of space,
fills up 200 MB with game stuff, and the remaining 200 MB contains whatever
was already there.
Does this make sense? You can try it with other large unfilled files on
your system and see the same thing."
So there you have it folks. Valve has absolutely no interest in your pornography collection or your indexed and alphabetized hoard of mp3s that would earn you an RIAA lawsuit quicker than you can say kazaa! ;)
News source: 3dnewz.com