Twitter’s iOS app experienced a subtle but important change Friday the old style of replies, which required placing the “@” character in front of the username of the person you’re replying to, was briefly gone, and replaced with the text “replying to” above the tweet.
Twitter quickly reverted the change, explaining on its Support account that it was an “experiment” which “accidentally” went out to all iOS users.
Today, an experiment around replies accidentally went out to everyone on iOS briefly. Upside, we got helpful feedback – we’re listening!
— Twitter Support (@Support) December 9, 2016
The new approach to replying had some unintended consequences; since the @ replies didn’t count against Twitter’s 140-character limit, you could add as many as you wanted in one tweet — and spam all those people in the process.