Ok, so I thought I'd update my hosts file with a load of servers that give you nasties:

127.0.0.1 coolwwwsearch.com
127.0.0.1 coolwebsearch.com
127.0.0.1 hi.studioaperto.net

etc...

However, the pages still load.
I noticed that there's two other hosts files:

hosts.bho
host (recognised as an iCalendar file)

could these be interfering?