Note that many websites have their own advertising, unrelated to adware.
An invasive Hijacker that copies multiple files and morphing startup entries on every boot to avoid detection and removal.
About:Blank as your homepage
Excessive pop-ups (normally porn related)
Randomly generated files names
This is quite possibly one of the most difficult kind of infections. Many times in order to get a computer completely rid of this pest, a professional spyware researcher must be consulted.