[caption id="attachment_11754" align="aligncenter" width="465"] A Vine posting.[/caption] Some 40 million people use Vine, according to an Aug. 20 Tweet from the video-sharing service. That number represents some pretty significant growth: in June, Vine revealed that it had 13 million users. That was right around the time that Instagram launched its own micro-video service, one seemingly designed to take Vine head-on. If Vine has seen its user base rise exponentially in the past two months, it’s a clear sign that Instagram’s foray into its territory didn’t work. (Of course, only a small portion of those 40 million people may actually use the service on a daily or even monthly basis—but Vine is counting them nonetheless.) Vine-versus-Instagram is actually a proxy battle in a much larger war between Twitter (which released Vine) and Facebook (owner of Instagram). Although Twitter lags Facebook with regard to total users, the micro-blogging service has been rapidly catching up over the past several quarters, with GlobalWebIndex recently suggesting that its number of active users had increased 42 percent between the second quarter of 2012 and the first quarter of 2013. The war between Twitter and Facebook has rumbled on for some time. In December 2012, Facebook disabled Instagram’s integration with Twitter, robbing the latter’s users of the ability to view Instagram images directly on the service. Facebook’s move irritated a number of pundits, who viewed it as an attempt to restrict social-network interoperability in the name of profit. “The only way these companies can succeed financially is by tricking members and forcing them into walled gardens,” Dan Lyons wrote in a Dec. 10 ReadWrite posting. “Think of it this way—there’s a reason that they don’t hold a circus out in the open, and instead put it under a tent—and it’s not to keep you dry in case of rain.” That criticism didn’t stop Instagram from firing again at Twitter, this time with its own micro-video app. But if the current numbers are any indication, that fire didn’t really seem to harm Twitter (or Vine).   Image: Vine