when my bandwidth was high

I got an email this morning telling my bandwidth for the month was at 75%. It’s never that high! I dug through my referrers looking for someone somewhere direct linking, but couldn’t find anything major (btw, I hate the new referrer program my webhost uses – on forums, it doesn’t record the actual URL it came from, just the top page of the forum, so it’s impossible to find where on that forum I’m being linked).
I’ll make it to the end of the month, but that was strange.