maybe this will help you Deepak > http://googlewebmastercentral.blogspot.co.uk/2012/10/a-new-tool-to-disavow-links.html
Using this tool you can tell Google that a particular link is not related to your website. You can use it if you think some page on internet is harming your rank on Google.
Most people on this forum believe it's simply for removing links until Google fixes your ranking. However, that's not the case. While I've seen countless people run around on this forum, suggesting that a webmaster's first stop to fixing a ranking decline is to start throwing random links in the disavow tool (some of the worst advice I've ever seen, on any forum, anywhere), that's not what it's for at all. The Disavow Tool should be used for combating negative SEO attacks, nothing else.
Thanks to all for there valuable replay, Now i have much more information about Google disavow tool. Pleas keep it on and share your valuable answer and information, Thanks!!!
I think the most important advice I've seen for the Google Disavow tool is from Google's own blog post for it. http://googlewebmastercentral.blogspot.com/2012/10/a-new-tool-to-disavow-links.html
This support article by Google on its Disavow tool is very informative & will be very helpful for you. Also don't forget to read this interesting article on how to use this tool right away.
It takes some time for Google to take negative links down. I caught competition doing extremely bad SEO against my clients website. Traffic dropped and client is frustrated. Now we work on building good links to overpower the bad ones. One of my own website had this issue, but since it had higher rankings no damage has been done. The websites that do get hurt are usually ones that are hanging on thread. My opinion is that Google should extensively ignore all low value negative links. No reason to hurt website owners since there is no proof. Another issue is finding your negative links. If your website has thousands of links it could be extremely hard to determine which links need removal.
The problem is that you can buy 100 negative links for $20. I could easily buy 1000 links and point them to my competitors URL. Google will never know who actually did this. As I said before Google should ignore all bad links, but I assume they have hard time finding which which "low quality" links are spam and which are genuine good links.