Twitter recently came under fire for releasing an iPhone app update with an obnoxious ad overlay, getting in the way of tweets. Twitter called it the "Quick Bar" but it quickly acquired a slightly more derogatory nickname.
After much public uproar, TechCrunch reports, Twitter has released another update that puts the ad bar at the top of the page, and not floating around covering important tweets.
If the new version doesn't appear in your update section, try searching for Twitter app in your iOS app store.