According to a Pandia article, Google is building a very large "rat trap" and using historical data to identify search engine spammers. So, if you were a spammer in the past or ever tried any so-called "black hat techniques" to manipulate a website's search engine rankings, it might come back to haunt you.
"You probably already know that engines are striving to deliver results based on your prior searches. But what a lot of people are missing is that search engines are building a database of every website’s, every company’s and every SEO’s optimization efforts.
As we speak, Google is building a very large rat trap and temporarily nourishing all of the rats who are eating the bait-cheese. Google wants you to join the various linking, advertising, and article-content networks so they can identify all the rat-trails and trap the rodents en masse."
So how do you think they're identifying former black hatters?
Google keeps copies of its own search index. If it grows suspicious of your search engine optimization techniques, it may go back into its archives and see what your site (or even you as a registered web site owner) did years ago.