Google announced that it is changing the way it categorizes link data in Webmaster Tools.
"As you know, Webmaster Tools lists links pointing to your site in two separate categories: links coming from other sites, and links from within your site," says Google Webmaster Trends analyst Susan Moskwa. "Today’s update won’t change your total number of links, but will hopefully present your backlinks in a way that more closely aligns with your idea of which links are actually from your site vs. from other sites."
For one, subdomains are now counted as internal links, which makes a great deal of sense. Here's a chart showing how links have changed:
"If you own a site that’s on a subdomain (such as googlewebmastercentral.blogspot.com) or in a subfolder (www.google.com/support/webmasters/) and don’t own the root domain, you’ll still only see links from URLs starting with that subdomain or subfolder in your internal links, and all others will be categorized as external links," says Moskwa. "We’ve made a few backend changes so that these numbers should be even more accurate for you."
She does note that if you own a root domain, your number of external links may appear to go down.