Google on Friday said it has made it harder for spam-packed websites to rank high in results at the world's top Internet search engine.

While the amount of "webspam" in query results is less than half of what it was five years ago, the California-based Internet firm has seen a "slight uptick" in recent months, according to Google principal engineer Matt Cutts.

"Webspam is junk you see in search results when websites try to cheat their way into higher positions in search results or otherwise violate search engine quality guidelines," Cutts explained in a blog post.

"We recently launched a redesigned document-level classifier that makes it harder for spammy on-page content to rank highly."

The new classifier better detects words or phrases typical of "junky, automated, self-promoting" comments repeated on pages at spam websites, according to the engineer.

Google also "radically improved" its ability to detect when legitimate websites have been tainted by hackers in the kinds of attacks that were a major source of spam last year, according to Cutts.

Other spam-fighting tactics being considered at Google include identifying websites laden with content copied from elsewhere on the Internet, he added.

Cutts stressed that having Google-powered ads on pages did not elevate them in search results or bar websites from repercussions of violating quality guidelines.