How accurate is link: search? Do links not in the list still get credit?

Matt's answer:

CUTTS: Sven Heß from Wiesbaden, Germany asks, “How accurate is Google’s backlink check (link:…)? Are all nofollow backlinks filtered out or why does Yahoo/MSN show quite more backlink or more results? The short answer is that, historically, we only had room for a very small percentage of backlinks because web search was the main part and we didn’t have a ton of servers for link colon queries. And, so, we have doubled or increased the amount of backlinks that we show over time for link colon, but it is still a sub-sample, it’s a relatively small percentage. And I think that that’s a pretty good balance because if you just automatically show a ton of backlinks for any website, then spammers or competitors can, you know, use that to try to reverse-engineer someone’s ranking. And you don’t necessarily want some else spying on your rankings and trying to figure out how they can compete with you by getting every single link that you got. What we do instead is a nice compromise. If you registered your site in google.com/webmasters, our webmaster console, then you can see all, or practically all of the banklinks that we know about you. So, a vast, vast, vast, you know, majority of the banklinks that we know about are there in Google’s Webmaster console. So, you can look at a sub-sample for any website or any page on the web, but if you want to see pretty much the full dump of what we know about, you can see it for your own site but not necessarily for your competitors. We think that that’s a pretty good compromise, and so that’s probably the policy that we’ll have going forward. San Diego, Tim from San Diego says, “If you have inbound links from reputable sites but those sites do not show up in a link:webname.com search, does that mean you are not getting any credit in Google’s eyes for having those inbound links? No, it doesn’t. Link colon only shows a sample, you know, a sub-sample of the backlinks that we know about. And it’s a random sample, so it’s not like we only show the high page rank backlinks–that’s what we used to do–and then anyone who had a page rank four or below wasn’t able to see their backlinks because their weren’t in the high page rank, they weren’t getting high page rank links. So we made it more fair by randomizing which backlinks we would show and we also sort of doubled the number of backlinks that we would show at that time. Now, what’s interesting is if you only show links that flow rank or that we trust or that are, you know, don’t have a nofollow, then people could kind of reverse-engineer that and say, “Oh, I’ll try to get the links that are really valuable.” So, we show the links that do, you know, carry a lot of credit in our system and we also show the links that we don’t really trust or don’t really carry a lot of credit in our system. So, it is truly just a random sample of, you know, stuff that’s nofollow, stuff that’s followed, stuff that we do believe a lot, stuff that we don’t trust as much. So, just because you don’t see one particular link and link colon, it doesn’t mean that it doesn’t or does flow–reputation, page rank, whatever you want to refer to it as. If it’s your own site, you can use Google’s Webmaster console, sign up, and get a very complete, basically, the vast majority of links that we know about as a dump that you can even download it as a CSV file. So, if you do want to get a really good idea of your backlinks, that’s the place to go and get a pretty exhaustive list of your links according to Google.

by Matt Cutts - Google's Head of Search Quality Team

Original video: