With the latest changes to its search algorithm, Google is aiming to reward Web sites that offer original, in-depth content at the same time that it penalizes those that simply borrow content from others.

Rolled out this week, the changes will help ensure that sites considered to be of "high quality" will rank higher in Google's search results, while those deemed of "low quality" will get dumped lower in the ranks, according to a blog posted yesterday by Google fellow Amit Singhal and principal engineer Matt Cutts.

Google is clearly looking to crack down on "content farms," sites that purposely tailor their pages with content that often makes little to no sense but is loaded with keywords and other information designed solely to generate a huge number of hits.

How does Google figure out which sites are high-quality and which ones aren't, especially since that sort of determination can be subjective

Singhal and Cutts explained in general terms that sites with original information, such as research, in-depth reports, and thoughtful analysis would be looked upon more favorably, while those that offer low value-add, that copy content, or "that are just not very useful" would be in the doghouse. And the criteria used to make this determination are part of the new algorithm.

A spokesman for Google told CNET today that the company can't share the specifics of how the algorithm works because "we don't want to give bad actors a way to game our algorithms and worsen the experience for our users."

The company said that the new rankings won't rely on feedback obtained from its Personal Blocklist, a new Chrome extension that tracks which Web sites are blocked by users and then sends those results to Google. But the company said it did compare the information from the Blocklist with the sites caught by the new algorithm and found that many of them popped up in both places. Specifically, 84 percent of the top dozen domains flagged via the extension have also been caught by the tweaked algorithm.

For now, Google has deployed these changes only in the U.S. but plans to roll them out in other countries over time. The company is also promising further updates that it thinks can further improve its search results.