Looks like the popular Digg This WordPress plugin had a security hole enabling spammers to fake a HTTP referral like they were coming from Digg and plant a Digg button to their article and not yours right on your blog. Wouldn’t that suck? You think you’re getting Diggs and readers think they’re digging your article only to promote spammers.
Be sure to get the Digg that plugin and also spread the word by digging the Digg article below.
UPDATE: The problem’s fixed. Get it here.