FOR some time, Google has been threatening to make life harder for so-called "content farms", which produce mountains of low-grade articles stuffed with popular keywords, to ensure that they appear high up in search results. Google users grumble at having to wade through reams of such articles to find ones that are really informative. Now the search giant has revealed that it has tweaked the secret formula that it uses to rank web pages in ways that it hopes will make life harder for the purveyors of such spam.

The changes to Google's alogorithm algorithm, which will affect some 12% of the queries that its search engine handles, come in response to a growing chorus of criticism from some Google users. A number have publicly accused the company of being slow to crack down on content farms such as Demand Media and Associated Content because Google benefits from the revenue generated by the ads served up alongside the anodyne content they churn out. "Google has become a jungle: a tropical paradise for spammers and marketers," lamented Vivek Wadwha, an entrepreneur-turned-academic, in a recent blog post. 

Other critics, such as Paul Kedrosky, a blogger, have given warning that people may look for new ways to find relevant information on the web if Google cannot get to grips with its spam headache. And search-engine rivals have been doing their best to profit from the company's discomfort. Blekko, a start-up that allows people to hunt for information online in narrow vertical categories such as "health" and "finance"—and to highlight and block any rubbish that creeps into its results—has even launched a "spam clock" that underlines the volume of spam being produced on the web every day.

Some observers caution that criticism of Google may be overdone, pointing out that users are not in fact deserting the search engine in droves. Google itself claims that its ability to serve up relevant content fast has never been greater. That may be true, but the search giant clearly feels the need to clean house now rather than risk seeing more of its results pages turned into Augean stables of spam. It has also added functionality to its Chrome browser that lets people block specific sites from search results. The battle with the content farms has begun.