Recent to Sky broadband? Not a parent? Might want to turn this off.

Login to your My Sky iD and set this to off.

If your a parent, turn it on for added child protection.

http://www.sky.com/products/broadband-talk/sky-broadband-shield/features/

I've also seen TalkTalk. Although I'm unfamiliar with how that works it has a separate option for ISP level virus protection that can be enabled separate to the content filter which is interesting.