No it’s not something out of a Mission Impossible movie where if you get caught Google will disavow any knowledge of you. It is a tool that helps webmasters deal with unnatural backlinks that may be part of a negative SEO attack.
The disavow tool is used to advise Google to ignore any links you tell it to. The next time that Google crawls the links you disavow they essentially add an invisible nofollow tag to it.
When it was first launched in October 2012, Google advised that the tool should be used only if a warning had been issued by Google. Presently, according to Google’s Matt Cuts that is no longer the case. He states that webmaster should go ahead and use the disavow tool when they are alerted to bad backlinks. You no longer have to wait for Google to give you a warning.
“If you are at all worried about someone trying to do negative SEO or it looks like there’s some weird bot that’s building up a bunch of links to your site and you have no idea where it came from, that’s the perfect time to use disavow as well,” Cutts said. “I wouldn’t worry about going ahead and disavowing links even if you don’t have a message in your webmaster console.”
The message here is to pay attention to your backlink profile and take action sooner rather than waiting to hear from Google.
But keep in mind that the Disavow tool is not the only answer, nor is it an all encompassing solution. You have to make a good faith effort to remove links beyond just using link disavow. And a warning comes with the disavow tool… “The disavow tool is an advanced tool and should be used with caution. Using it improperly has the possibility to do harm to your site.” Consulting with an experienced SEO may be a good idea. Staying up with the latest SEO changes can also help.