A rumor says Microsoft may buy Yahoo. Microsoft should run the other way.

A rumor making the rounds says that Microsoft is once again seriously considering buying Yahoo. Of all the bone-headed moves Microsoft could make, doing that would be the top of the list. Microsoft should run the other way.

BusinessInsider reports that an unnamed source working for the Microsoft portal MSN claims that "Definitely, people are talking" about buying Yahoo.

The source disparaged the idea of buying AOL, but then added:

"Yahoo is a lot more interesting. If it comes into play, then at least their U.S. media business is a pretty interesting asset."

The source claims that Microsoft might buy Yahoo as a way to beef up MSN, because "MSN is a critical component of helping Bing win."

The rumor surfaces at a time when investor Silver Lake is believed to be considering buying Yahoo. Bloomberg reports that Silver Lake may buy Yahoo, sell off Yahoo's Asian assets, and then either try to turn the remainder of Yahoo around or attempt to sell it.

Microsoft shouldn't enter into the bidding for Yahoo. Buying Yahoo would get Microsoft very little. Microsoft would pay billions for a Web property that has been sinking for years, and shows little hope of success. Microsoft would be getting a demoralized company with plenty of demoralized staff. In addition to the billions that Microsoft would pay for Yahoo, Microsoft would be forced to spend plenty of time integrating Yahoo, at a time when Microsoft needs to focus as much of its efforts as possible on mobile and Windows 8. Yahoo is yesterday; mobile and Windows 8 are tomorrow.

As for how reliable the MSN source is, my guess is that the person is engaging in a lot of wishful thinking. Buying Yahoo would make MSN more relevant and possibly help MSN's flagging fortunes. But it wouldn't help Microsoft at all. My guess is that Microsoft will stay away.