Best way to remove it is to use ad-ware from Lavasoft. It's free, it's fast and it worked for me.
It's available at:
http://www.lavasoft.de
It's also worth downloading RefUpdate from them as well, as this keeps all the ad-definition files up to date (v. much like anti-virus update).
There's a switch in the program to remove lop.com.
HTH,
Justin
P.s. you'll probably be in for a nasty shock when you run it for the first time.