Google is thought to have rolled out an update to Panda, the firm's algorithm that was aimed at improving search results but affected hundreds of sites' rankings.
Google Panda was released in April this year and was designed to reduce spam within the search results, while promoting sites with clear navigation and good content. However, many legitimate sites were misclassified by the algorithm and saw their traffic plummet.
At the Search Marketing Expo in Seattle earlier this month, Google's Matt Cutts said the search engine was working on Panda 2.2 .
"Don't consider it finished," he said. Google will continue making improvements at least through the end of the year, he said.
According to Pocket-lint, websites owners have been swamping SEO forms to complain they've been pushed down search results, while others have seen their rankings soar and are appearing higher up in search results.
Google has yet to respond to comment on the matter.