Twitter banned third-party advertising yesterday, but the exact nature of the ban is still unclear. Twitter, in its initial blog post, said "we will not allow any third party to inject paid tweets into a timeline on any service that leverages the Twitter API." But since that's incredibly vague, Twitter also mentioned that the ban would be laid out more precisely in the Twitter Terms of Service, which will be updated shortly.
In the meantime, one in-stream advertiser, IZEA, has responded already. But the biggest names, Ad.ly and TweetUp, remained silent until just now, when the former issued a brief statement. Ad.ly, which lets advertisers essentially rent highly read tweets (you'll see, say, a McDonald's ad tweeted by Kim Kardashian) one at a time, insists they're not affected by the ban. The statement:
"Since inception, Ad.ly has, and still is operating under Twitter's approved guidelines and terms of service for advertising on its platform. We look forward to continuing to create long term value for our advertisers and publishers, both of whom are key constituents in the stream ecosystem."
So essentially, Ad.ly is claiming that they won't be affected by the new ban, which for all we know at the moment might be true. We've got to assume they've cleared that statement with Twitter—they waited a day, so they must have made sure their response is factually accurate.
It's awfully hard to tell exactly what Twitter's banning: Banner ads in third party apps like Twitterific and TweetDeck aren't affected, and now Ad.ly claims paid tweets aren't, either. We'll continue talking with other third-party advertisers to see who exactly is left out in the cold.