Website Logs Question - who is adv-adserver.com?

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I monitor my website logs throughout the month, and a peculiar referring domain has recently (last 2 or 3 months) risen to the top of the pile.

adv-adserver.com is now my number 1 referring domain. I tried to dig for what that is, but I'm getting absolutely nowhere. It's from a server located in San Antonio, TX. Here's the whois info:

http://www.ip-adress.com/whois/adv-adserver.com

Anybody have any ideas? Like I said, it is now my number one referral, and I just want to know who/what it is. Does anybody else have this pop up in their logs?

Thanks!

Jeff