The Federal Trade Commission is actively investigating Twitter and the way it deals with the companies building applications and services for its platform, we've learned.

In Spring 2010, Twitter started making noises that it planned to provide users "official" versions of services that, until then, had typically been provided by third-parties – ads, photo-sharing, URL shortening and mobile apps.

Over the following year, Twitter followed-up on its promise. It acquired third-party Twitter clients such as Tweetie and TweetDeck, blessing them as "official" Twitter apps.

Meanwhile, serial entrepreneur Bill Gross – best known for inventing search advertising – launched a company called TweetUp. The initial plan was some kind of Twitter ad network. Later, Gross started buying Twitter apps.

Eventually, his company got funding from Accel with the idea that the money would be used to buy TweetDeck. It sort of looked like Gross might be planning to launch a Twitter competitor – or at least string his Twitter clients into their own monetized network.

But then Twitter got aggressive with Gross – first by shutting down his app UberTwitter for three days, and then by stepping in and acquiring TweetDeck for itself.

Twitter and the FTC declined to comment.

A representative from Gross's company tells us: "We have been contacted by the FTC and are in the process of responding to their requests."

Another app-maker says: "Our lawyer has advised us not to talk about this particular topic."

Today, we learned that Twitter will soon create a site to "offer up as much information as possible to developers and partners." The news seems related.

Twitter settled with the FTC in March over allegations of privacy violations.

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