updated 07:20 pm EDT, Tue October 16, 2012
Sites can now block link spam
Google has introduced a new tool allowing site operators to "disavow" links to their site. The tool is aimed at cutting down on link spam in Google search results and helping site operators respond to notifications of "unnatural links" that may point to their sites. Users taking advantage of the tools will now be able to follow a process whereby they can upload a file containing a list of any links they want to disavow.
Google detailed the new tool in a post on the Official Google Webmaster Central Blog. The post lays out the disavowal process in detail, and the head of Google's web spam team, Matt Cutts, recorded a ten-minute video explaining the process in greater detail (seen below).