Corporate instant messaging has been big news lately, but yesterday there was word on a more general move that makes some techie types edgy. According to CNET, Yahoo! (NASDAQ:YHOO) is blocking third-party instant messaging clients like Trillian from its network. If you're sick of a trillion spam messages flooding your email inbox, that's the reason Yahoo! supplied for saying no to Trillian.

Programs like Trillian allow their users to instant message people who use different messaging options, such as Yahoo! Messenger or the popular AOL Instant Messenger (AIM), which is offered by Motley Fool Stock Advisor pick Time Warner's (NYSE:TWX) America Online unit. It's likely more people than you realize could be using Trillian when they chat with you online.

According to Yahoo!, the reason for the move is to head "spim" off at the pass. Spim is the IM equivalent to spam, one of the monster headaches of the Internet. Spam's even caused the heavyweights noted above as well as Microsoft's (NASDAQ:MSFT) MSN and EarthLink (NASDAQ:ELNK) to form an anti-spam squad, making rivals unlikely allies out of sheer necessity.

Whereas email is an open communication tool -- and the recent email wars have added up to a real plus for consumers -- IM remains relatively balkanized, with no compatibility between the different products unless you use a program like Trillian. (I personally see the lack of compatibility, or an open standard, as a hindrance to growth for players like Yahoo! and MSN, though there's the argument that the programs retain users -- and eyeballs for advertising and potential product upsells -- through their closed natures.)

From the Yahoo! point of view, sure, nobody wants to dodge enlargement, mortgage, or medication ads through IM, seeing how one theory for IM's runaway success has been email fatigue from endless misspelled, inappropriate, word-salad spam marketing. It's a threat to keeping customers.

This isn't the first time Yahoo! and the rest have blocked third parties, and techies say it won't be long before a patch restores communications. On the other hand, last I heard, AIM still possesses about half of the instant messaging market. If Trillian, Gaim, and other users get sick and tired of the ongoing block-and-patch game, given AIM's critical mass of IM users -- which, without compatibility, transforms into a form of free, word-of-mouth, viral marketing -- maybe AOL stands the most to gain.

What do you think of Yahoo!'s move? Do you use Yahoo! for some things, but not for others, like messaging? Talk to other Fools on the Yahoo! discussion board.

Alyce Lomax does not own shares of any of the companies mentioned.