A recent Google search by Durante Windows & Siding, in Irondale, Ala., yielded a startling result: An ad popped up offering a free estimate from “Durant Windows.”

“We clicked on it,” marketing manager Daniel Gallegly says, “and it took us to a landing page asking for contact information.” Gallegly figured out that the overseas company behind the ad generated leads and sold them to home improvement companies.

After being confronted, the company apologized and removed the ad. But who knows how many leads that tactic cost Durante Windows.

That said, Durante, like most large home improvement companies, bids on competitors’ names as keywords, so that a homeowner looking for the competing company will also find an ad for Durante along with the requested search results. The difference, Gallegly notes, is that Durante doesn’t present itself under a competitor’s name. “We just say, ‘Call Durante, get a second opinion.’” He compares it to Yellow Pages advertising.

If you use this online marketing tactic, consultant David Alpert of Continuum Marketing offers a heads-up: It’s illegal to use another company’s trademarked name in your ad. In other words, you can bid on a competitor’s name as a keyword, but you can’t use that name in the text of your ad.

So, is bidding on competitors’ names effective? It’s usually not as successful as overall search marketing, Todd Bairstow, founder of Keyword Connects, in Boston, says. “But if you don’t do it, your competitors ... or a third-party competitor will do it to you. So it’s something every company has to look at.” While the strategy of bidding on keywords is effective, Bairstow warns against depending on it. “You have to diversify your keyword list,” he says.

Diane Kittower is a freelance writer-editor in Maryland.