The site used by the killer (www.killwithme.com) actually existed. It was owned by the movie studio and it was used to promote the movie. In it, users were taken to a replica of the FBI computer used by the character Jennifer Marsh. Her desktop gets hacked by the killer who provides the visitor with four test he/she must complete to deactivate his site. The content has now been removed, and the domain name is available for sale or lease.
Colin Hanks' serial-dater character mentions Peggy the secretary as an upcoming date. This is a nod to Hanks' appearance on Mad Men (2007) - Hanks plays Father John Gill, a priest who becomes acquainted with Peggy the secretary (played by Elisabeth Moss).
When Jennifer finds the camera mounted on the car, you can see a brief clip from the blog section of killwithme.com and one of the comments, made by "clownz23", says she "holds a gun like a cop only hotter".