As Danial Ahmad suggests this action by the Pakistani government may be in retaliation of some bloggers posting (or reposting) the defamatory cartoons of the Prophet Muhammad which first appeared in a Danish newspaper.
Isn't it a tad bit ironic, though, that this ban went into effect after President George W. Bush left Pakistan after his hand-shake visit with Gen. Pervez Musharaf? Did the Pakistani government wait till the leader of the free world had departed their country before curbing people's rights? Imagine the PR romp if the censorship had occurred before W's visit. Yikes!