Rumors that Valve is planning on doing more with ultra-popular Warcraft III mod Defense of the Ancients All-Stars—or DotA—feel a lot less rumor-like now. The Half-Life developer recently trademarked "DOTA" for future use.
The developer of Team Fortress, Left 4 Dead and Portal filed a trademark request with the US Patent and Trademark Office last week, protecting "DOTA" for "Computer game software," "Electronic game software" and "Video game software." (Incidentally, Valve also applied for a "Portal" trademark of the same nature.)
While that's not confirmation that it actually plans on publishing the Warcraft III modification under its own name—Valve has plenty of trademarks that were never used for its games—the company's recent hiring of DotA Allstars developer "IceFrog" shows they have genuine interest in the game—or at least the design skills behind the game.