Phorm

If you're a BT Internet customer you may see a page like this come up in the next few days while you browse the Internub:

My advice to you would be to say 'no' and keep saying 'no' until you've changed your Internet service provider. Regardless of whether you say yes or no, if that page has appeared at any point then all un-encrypted HTTP (web) data you request on the Internet will be sent through Phorm's systems.
What's the problem with that? Phorm used to be known as 121media - peddlers of spyware, rootkits and all kinds of nasty shit, and BT is sending them every link you click, and every page you view.
Make you feel all warm and fuzzy? No. Me neither.

More at Dephormation, BadPhorm, and NoDPI.