Today, i login into admin panel & Go into customer->manage customer. The grid contain lists of customer but customer name column contain URL & in different language instead of english.
Yes, you have been "hacked" :D (Russians are too good for that ) . Check the suggested solutions from DependencyHell LINK
As first of the options i will suggest
Solution 4: Captcha (Magento or Google)
The russians bots have bypassed your registration form.