Microsoft started a metaphorical war with Google when it launched the Bing search engine two years ago. Yesterday it came close to becoming literal after Google told Danny Sullivan of Search Engine Land that it had gathered evidence that Bing was copying its search results.

In a kind of sting operation, Google rigged its own search engine last December to display certain results for a small set of nonsense search terms. When those same, fake, results began to sometimes be spat out by Bing in response to the same nonsense search terms, Google’s engineers concluded they had been robbed. Its equivalent to the maker of a map adding fake features so as to spot competitors ripping it off.

However, it seems more accurate to describe users of Internet Explorer and the Bing toolbar as the targets of Bing’s snooping, not Google. At least, that’s my read on what Microsoft’s head of search engineering Harry Shum said after Google’s principal search engineer Matt Cutts rounded on him Tuesday during a panel at an event on search technology hosted by BigThink in San Francisco.

“It’s not like we copy anything, we actually learn from the customer based on what they type and what they click on,” said Shum, “of course we track our users and what they do.”

Shum didn’t quite spell it out - no one at Microsoft has yet - but with those words and others he clearly suggested that Bing was tracking the activity of users across many websites with a view to improving Bing. It’s easy to see how some knowledge of what people are typing and clicking online could help build associations to boost Bing’s relevance. Because Google is such a big property using that tactic would of course capture a lot of interaction with their results. It also suggests that Bing may have some interesting data on how people use Facebook - the site that occupies more of US web time than any other.

Cutts countered Shum’s line by claiming that users were unaware that their data would be used in such ways, and would be unhappy with that if they found out. (It should be noted that Google’s own toolbar tracks plenty of information on web use and that the firm’s Google Analytics package tracks clicks from unsuspecting users for thousands of website that use it.)

For Web users the real question that emerges from this spat is not whether Google was copied, but whether you mind Microsoft watching your clicks.