Websites indulging in Negative SEO is not an unknown phenomenon. But Google wields its baton and penalizes the defaulters. Some time back many websites indulged in blackhat SEO and got down to buying innumerable links, to find an easy way to the top. But Google would have none of it and cracked down on the sites indulging in such malpractices. Following an update in its algorithm which helped Google identify such sites, a notice was sent out or in extreme cases, sites were penalized for having low quality or spam site links.
Of sites that got penalized, many honest ones opted to sweep out all the links acquired during that period. The Google Disavow tool is a god-sent for such mass clearance. Google understands the impracticality of removing all the links from spam sites and thus was invented this Disavow link tool. What you need to do is first identify all the links that you want to be ignored. Then you can enter in text form all the links from the concerned site or even the entire domain and upload it in the Disavow links tool. Once this is done, in a few days, these links are crawled and re-indexed by Google. It may seem tedious to identify all these unnatural links and get them removed; but to get back the lost credibility of your site it needs to be done. Such mass disavow of links may not be an easy job, but the effort does not go unnoticed by Google and your penalization may be lifted faster than it would have taken otherwise.
For new sites, or rather for recently acquired sites, the tool could be of great help as the domain may be a promising one but it may have lot of spam links connecting to it. The previous owners may have violated the norms and got those backlinks. So to start afresh, the webmasters could disavow all the links and start with a clean slate. And though not recommended always, this action can definitely impact a reconsideration request that they put in.
All sites do not need to use the Disavow links tool. Unless you are into aggressive SEO with lot of low quality or unnatural links coming in to your site, you may not need to use this tool. So exercise extreme caution while using the tool as you would not want to remove the good natural links which would be hard to acquire again, once lost. For the average sites which do not have too many spammy links, the method of writing to the webmaster to have the links removed would work just fine. Only in case of repeated requests if the links are not being removed, or if the webmasters do not pay heed, do they need to resort to using the Disavow links tool. So all is not lost if you got a notification from Google… to the rescue is Google Disavow Links tool…