There is huge update of Google on 17th Jan 2013
But Google has not announced this they have done any updates. Google said “It's not Panda. We asked around a little bit and didn't uncover any other likely suspects, but remember that Google launches over 500 algorithmic changes per year, so there are always small changes rolling out.”
But webmaster from UK and India were more hurt due to this unconfirmed update.
In UK more than 27% and in India more than 36% hunted by this update
Let me know if any one more know and see this updates