Plot hole: The FBI in the movie has the ability to "blackhole" an IP address, which makes that computer unavailable to the internet. If they can blackhole the computer acting as the web server, they could also blackhole the computer acting as the name server (DNS), thereby taking down the web site and preventing additional users from connecting.
Continuity mistake: The skull on the Killwithme website is an x-ray of Owen's father's head. In the movie, it was mentioned that the glasses were found on the roof by an employee, and was sold on some website. Why would the x-ray have the glasses on the face of the skull if they were not with the corpse?