A trojan that blocks various p2p sites browsing page has been released through out the internet. Its comparatively new in business.

This link will give detailed info :-
Trojan Blocks The Pirate Bay and Mininova | TorrentFreak

Symptoms:-
You are not allowed to enter p2p site instead redirected to login page. You cant even login and stuck there.

How to fix it :-
Open Windows Explorer (start->run-> type explorer.exe and press enter)

Click Tools -> Folder Options
Under View tab Select Show Hidden files and Folders and Uncheck Hide Protected System Files

Now
Go to x:\windows\system32\drivers\etc

Open hosts file in notepad. You'll see multiple entries of the sites you cant log on to. Delete those entries and save the file. Problem solved.