Remember when Yahoo! (NASDAQ:YHOO) and Google (NASDAQ:GOOG) were best buds? They respected each other's strengths and didn't abuse each other's shortcomings. Yahoo! had no problem producing Google's superior search engine results, while Google relished sending relevant traffic over to Yahoo!'s many offerings.

But Google got feisty -- one may even say greedy -- along the way. From Gmail to AdWords to maps, Google started rolling out online services that struck at the core of what Yahoo! was doing... and hit Yahoo! out of the park every time. What would Yahoo! do? If the only response it could muster was to cash in on its stake in Google, well, that would be a hollow victory.

Apparently, Yahoo! isn't going to go down quietly now that eBay (NASDAQ:EBAY) and Google are commanding larger market caps in the dot-com arena. And if you connect the dots just right, you see that Yahoo! appears to be gunning for Google's prime AdSense service juggernaut.

Earlier this week, pointed out that the personal blog of a Yahoo! product manager was serving up ads -- off the Overture server -- that looked suspiciously similar to AdSense contextual text ads.

Yes, Yahoo! has been providing its ads to third-party heavies all along. Advertisers on Overture have access to the well-heeled pages of Microsoft's (NASDAQ:MSFT), Time Warner's (NYSE:TWX), and InfoSpace (NASDAQ:INSP). But an obscure hobbyist site?

No, that kind of grassroots effort has been Google's stomping grounds for more than two years now. Is Yahoo! finally sticking its spreading knife into someone else's bread and butter?

If so, well done, Yahoo! This past quarter, nearly half of Google's revenue came from AdSense. Granted, that's what Google calls its entire third-party ad network, but ask any small or medium-size content site owner how AdSense has helped monetize their efforts with a steady stream of relevant ads, and you may need a bucket to catch the drool.

However, even the loyalists have been getting restless lately. Niche forums like are ripe with folks complaining that their AdSense payouts have been diminishing over the years. Whether that's because AdWords sponsors are bidding less on keywords or because Google is tweaking the revenue split formula, now would be the perfect time for Yahoo! to present an alternative product.

When Yahoo! announced that it was doing away with the Overture brand on Tuesday, the press release noted that the company will "continue to enhance and expand Yahoo!'s network of sponsored search distribution sites."

Although you could interpret that statement as a corporate goal to attract more of the larger, established sites it currently serves, Yahoo! is also hinting at the rollout of an AdSense clone. With the amount of love that Google is getting from webmasters these days, it certainly wouldn't be a bad thing to do. So when you do come to market with this, Yahoo!, do yourself a favor and bring a bucket. That drool can be awfully slippery.

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Longtime Fool contributor Rick Munarriz is a fan of both Yahoo! and Google. Although he would love to see them get along again, he thinks it's better for everyone that they've been trying to top each other lately. He does not own shares in any of the stocks mentioned in this story. The Fool has a disclosure policy. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early.