Your ISPs are planning to sell your browsing data to a 3rd party.
Cable Forum: Virgin Media signs targeted ad deal [Update 2]
The essence of the Phorm scheme is straightforward. It will have
equipment at ISPs that will track your activities on port 80 (used for
the web) - though not to secure websites. With each site you visit it
will capture the URL (and, for a search engine, the search terms too)
plus enough of the header data from the page to "categorise" it into one
of a number of areas. Anything longer than a three-digit number is
thrown away. Your IP address is not captured, but a cookie with a unique
number is set on your browser when you start using it, which persists
into the future.
Lots of discussion here:
Virgin Media Phorm Webwise Adverts [Updated: See Post No. 1, 77 & 102] - Cable Forum