Twitter makes a change in an effort to slow down spammers
In an effort to stop spammers from taking over Twitter, the social media app is limiting the number of followers that can be added to an account on a single day. Previously that number was 1,000 and a tweet from the Twitter Safety account (yes, that is a thing) reveals that the new cap is 400. This is supposed to prevent spammers from adding a large number of followers and then deleting them in a "bulk, aggressive or indiscriminate manner" that violates Twitter's rules.
By adding all these followers, spammers hope that the majority will follow them back. Those that do will soon find a number of spams in their timeline. Those that don't will soon be unfollowed by the spammers. This is a cycle that continues over and over again. In a series of tweets, Twitter's Yoel Roth explains that lowering the number of followers a day from 1,000 to 400 won't stop the spammers, but it will slow them down. The 400 limit will "make each spam account less effective, slower, and more expensive to operate."
Roth adds that Twitter decided to make the new cap 400 because it allows people to follow the accounts they're interested in while it stops the most spam. Almost half of the accounts that were following 400 Twitter users per day were engaged in churning, which is defined as "repeatedly following and unfollowing the same accounts" in an attempt to grow the number of followers that a Twitter subscriber has. He adds that 99.87% of Twitter use will be unaffected by this new rule.