After months of anticipation, Google’s Matt Cutts, at PubCon in Las Vegas today, finally announced a new tool in Webmaster Tools to disavow links.

Cutts made comments at SMX Advanced back in July, indicating that a tool would be on the way, and it is now here.

In text on the tool itself, Google says, “If you believe your site’s ranking is being harmed by low-quality links you do not control, you can ask Google not to take them into account when assessing your site.”

Here is Cutts talking about it in a new Webmaster Help video:

“You might have been doing blog spam, comment spam, forum spam, guestbook spam…maybe you paid somebody to write some low quality articles and syndicate those all over the place with some very keyword rich anchor text, and maybe Google sent you a message that says, ‘We’ve seen unnatural links to your site or we’ve taken targeted action on some of the unnatural links to your site,’ and so as a result, you want to clean up those backlinks,” Cutts says in the video.

First and foremost, he says, they recommend getting those links actually removed from the web. Of course, that’s easier said than done.

Google says in a help center article:

PageRank is Google’s opinion of the importance of a page based on the incoming links from other sites. (PageRank is an important signal, but it’s one of more than 200 that we use to determine relevancy.) In general, a link from a site is regarded as a vote for the quality of your site.

Google works very hard to make sure that actions on third-party sites do not negatively affect a website. In some circumstances, incoming links can affect Google’s opinion of a page or site. For example, you or a search engine optimizer (SEO) you’ve hired may have built bad links to your site via paid links or other link schemes that violate our quality guidelines. First and foremost, we recommend that you remove as many spammy or low-quality links from the web as possible.

If you’ve done as much work as you can to remove spammy or low-quality links from the web, and are unable to make further progress on getting the links taken down, you can disavow the remaining links. In other words, you can ask Google not to take certain links into account when assessing your site.

Update: Google has now put out an official blog post about the tool. In that, Webmaster Trends Analyst Jonathan Simon writes:

If you’ve ever been caught up in linkspam, you may have seen a message in Webmaster Tools about “unnatural links” pointing to your site. We send you this message when we see evidence of paid links, link exchanges, or other link schemes that violate our quality guidelines. If you get this message, we recommend that you remove from the web as many spammy or low-quality links to your site as possible. This is the best approach because it addresses the problem at the root. By removing the bad links directly, you’re helping to prevent Google (and other search engines) from taking action again in the future. You’re also helping to protect your site’s image, since people will no longer find spammy links pointing to your site on the web and jump to conclusions about your website or business.

If you’ve done as much as you can to remove the problematic links, and there are still some links you just can’t seem to get down, that’s a good time to visit our new Disavow links page. When you arrive, you’ll first select your site.

According to a liveblogged account of Cutts’ speech, he says not to use the tool unless you’re sure you need to use it. He mentioned that Google, going forward, will be sending out more messages about examples of links Google is distrusting. He also says not to disavow links from your own site.

Regarding those link messages, Cutts says in the video that these are only examples of links, and not a comprehensive list.

The tool consists of a .txt file (disavow.txt), with one URL per line that tells Google to ignore the site. You can also use it to block a whole domain by using a format like: domain:www.example.com.

Cutts apparently suggests that most sites not use the tool, and that it is still in the early stages. Given that link juice is a significant ranking signal for Google it’s easy to see why Google wouldn’t want the tool to be over-used.

It can reportedly take weeks for Google to actually disavow links. In a Q/A session, according to the liveblog from Search Engine Roundtable, Cutts said you should wait 2-3 days before sending a reconsideration request after you submit a disavow file. When asked if it hurts your site when someone disavows links from it, he reportedly said that it typically does not, as they look at your site as a whole.

Danny Sullivan blogs that “Google reserves the right not to use the submissions if it feels there’s a reason not to trust them.”

Users will be able to download the files they submitted, and submit it again later with any changes. According to Sullivan’s account, Cutts said the tool is like using the “nofollow” attribute in that it allows sites to link to others without passing PageRank.

That’s good to know.

A lot of SEOs have been waiting for Google to launch something like this for a long time. Perhaps it will cut down on all of the trouble webmasters have been going through trying to get other sites to remove links. At the same time, we also have to wonder how much overreaction there will be from webmasters who end up telling Google to ignore too many links, and shooting themselves in the foot. This will be a different era, to say the least.

Just be warned. Google’s official word of caution is: ” If used incorrectly, this feature can potentially harm your site’s performance in Google’s search results. We recommend that you disavow backlinks only if you believe you have a considerable number of spammy, artificial, or low-quality links pointing to your site, and if you are confident that the links are causing issues for you. In most cases, Google can assess which links to trust without additional guidance, so most normal or typical sites will not need to use this tool.”

The information Google uses from the tool will be incorporated into its index as it recrawls the web and reprocesses the pages it sees.

Google currently supports one disavow file per site. That file is shared among site owners in Webmaster Tools. The file size limit is 2MB.