“THE Google brand has taken on a life of its own,” concedes Jim Lanzone, the boss of Ask.com, the fourth-largest but fastest-growing search engine, and this simultaneously frustrates and delights him. It frustrates him because people say they “google” things even when they go to Ask or other engines to search the web; because Google is considered, for no good reason (in his opinion), “the safe choice under pressure”; and because many people “don't seem to want choice” and stick to Google out of mere inertia.

But it delights him, because Google, having made many enemies, must now fight many battles; and because Google, perhaps out of hubris, appears to be getting distracted. This month, for instance, Google unveiled a free online spreadsheet program, which, like many Google products, has little to do with web search and is meant to needle Microsoft, the world's largest software company, which has a near-monopoly on spreadsheets through Excel. Google, in other words, has impressive momentum, says Mr Lanzone, but a good martial-artist can use his opponent's momentum to overcome him, so “we're using search aikido.”

In terms of momentum—mass times velocity—Google's lead indeed looks daunting. It has by far the most mass, with an American market share of 43% as of April, which reaches 50% counting AOL, an internet property that uses Google's search technology. This compares with 28% for Yahoo!; 13% for MSN, which belongs to Microsoft; and 6% for Ask, which is owned by IAC/Interactive Corp, a conglomerate of about 60 online media brands. Google also has velocity: its market share grew by 17% in the four quarters to this spring, whereas Yahoo! and MSN both lost share. Only Ask has more velocity—its share grew by 35%—but then again it has little mass.

There are also other, even smaller search engines, such as Clusty.com, a service that displays results in thematic bundles, and SNAP.com, an engine founded by Bill Gross, a pioneer in the industry. But because barriers to entry in the search business are high—the engineering talent is limited and data centres that can simultaneously support millions of searches are expensive—most analysts think that the four big search engines will stay ahead of the tiny ones. The industry is young and switching-costs for users are low (a click, in effect), so there is still the potential for a change in leadership among these four. The contest is fierce, because search results, which display highly targeted advertisements, are the most lucrative pages on the internet.

Comparing the quality—that is, the relevance—of search results is highly subjective, but for the past six years or so Google has probably proved the best at the job. The stroke of genius of its two founders, Sergey Brin and Larry Page, was the PageRank algorithm, which treated the links to web pages as votes conferring authority, just as the best academic papers tend to get the most citations in other research. Google's problem today, says Chris Sherman, the executive editor of SearchEngineWatch, an online industry newsletter, is that “they regard themselves as the best, and yet they don't really seem to have a clear strategy,” which seems to make them dabble aimlessly.

Yahoo!, the largest internet portal with about 400m users (of its e-mail, instant-messaging, music and other products), has spotted this weakness and come up with a strategy to differentiate its own search engine. Yahoo! has been at this game for only two years—it used to use Google for its search technology, until it realised that this was the most profitable part of the business—but now has hundreds of engineers working on it. In contrast to the quasi-religious faith that Google places in its mathematical algorithms, says Eckart Walther, one of Yahoo!'s search bosses, Yahoo! is “about combining the best of people with the best of technology”.

The idea, Mr Walther says, is to “look not only at links between websites but also links between people” and thus to use “social search” to solve “subjective” queries. Caterina Fake, who came to Yahoo! as the co-founder of FlickR, a popular photo-sharing site it bought last year, gives the example of her own search for a lamp shade. A Google search returned lots of lamp stores, but all in generic styles. A search on Yahoo!'s “MyWeb”, by contrast, took into account the eclectic tastes of her friends and came up with the more fashionable, unconventional lamp shade that she was after.

This approach has potential, but also limits. The user has to be known to Yahoo! (ie, logged in) and the results are best when users do a lot of work—by, for instance, “tagging” things they see on the web with descriptions (“cool lamp shade”) so that online friends can benefit from these trails of “metadata”. But most people don't want surfing the web to feel like work, so the metadata is limited. To Mr Lanzone at Ask, the Yahoo! approach sounds like “a long walk for a short beer.”

So Ask—which used to be called Ask Jeeves but dropped Jeeves, a knowing butler, from its logo in February—is taking a different tack. It has come up with ExpertRank, an algorithm that also ranks web pages by incoming links, but is different from Google's PageRank in that it first groups, or “clusters”, pages and links by theme. So instead of using a web page's overall popularity to calculate its ranking, it finds the pages that are most popular among experts on a particular subject, a method that often returns better results than Google's. Ask also uses these thematic clusters to suggest the best ways to narrow or expand a search, a feature called “zoom” that is very popular.

Chris Sherman of SearchEngineWatch thinks that Ask is as good as Google for general web search—but better than Google for finding online maps and images. Ask, he thinks, is therefore starting to resemble Apple in the computer industry, which has a small but dedicated following of fans who consider the Macintosh operating system superior to the dominant Windows system by Microsoft (a comparison that is sure to make Messrs Brin and Page at Google cringe).

As for Microsoft, it has identified Google as a mortal threat to its business and has launched an all-out effort to catch up in online services in general, and in search in particular. Last winter, it tried to buy itself market share by negotiating with AOL for a merger—or at least an agreement under which AOL would switch from Google's search technology to MSN's; but Google pre-empted Microsoft and itself took a defensive stake in AOL. Microsoft has also hired former rivals who are well respected in the industry, such as Ray Ozzie, an innovator best known for inventing Lotus Notes, a collaboration programme, and Steve Berkowitz, Mr Lanzone's predecessor at Ask, who now oversees the MSN portal. Mr Sherman at SearchEngineWatch says the quality of search results on MSN so far “seems to be all over the map”. But, as he points out, Microsoft has a history of coming late to a market with a mediocre copy-cat product that gradually gets better until it prevails. The search-engine battle is not over yet.