Twitter has updated its developer guidelines, and one item stood out, "automated following or bulk following is also prohibited."
we relaxed some display requirements around author’s name, timestamps and permalinks; we clarified that the “no commingling” term doesn’t apply to manually curated streams; and, we now require developers to disclose their privacy policies before people download, install or sign up for a service. We have also clarified some restrictions: hosting datasets of raw Tweets for download is prohibited, and automated following or bulk following is also prohibited. Twitter Prohibits Automated Following or Bulk Following [dev.twitter.com]