Update - 11:05 EDT - The login issue has been resolved, and the a new version of Foursquare (7.0.5) is now available for download in the App Store.
Please update your app to the latest version if you’re experiencing any login issues.
Thanks to everyone while we worked through a fix.
6:03pm EDT - Users who have downloaded the latest version of Foursquare (7.0.4) on iOS released on 3/11/14 are unable to login to the app.
While we fix the issue we’ve temporarily removed the app from the App Store. We expect to have this resolved and available for download again very soon.
Please check this site for continued updates and thanks so much for your patience while we work on a fix.