or.... you (for some reason) have wildcard DNS added to your http server config. i.e abcd.domain.com and qwer.domain.com (or anything else you can think of .domain.com) will load the same website
Update: Yes you DEFINITELY have wildcard DNS activated, i just tried http://abc.xdame.com/ and it is the same site
Thanks for shading some light into this. I was getting a bit worried.