Though mainly a response to Twitter spammers, use of third party follow/unfollow tools is still permitted.
Twitter recently updated their Twitter API Frequently Asked Questions to include an entry explaining their decision to disallow bulk following and bulk unfollowing.
“Why are automated and bulk following/unfollowing services not allowed?
First, it’s worth clarifying that this policy change isn’t meant to prevent developers from building tools that surface potential accounts to follow or unfollow (like ManageFlitter's Unfollow tool). However, the follow/unfollow action must happen one account at a time, not in bulk.
After hearing feedback from users who rely on third-party tools for follow management, we want to provide more context behind this policy change. Per theTwitter Rules, following or unfollowing large amounts of users in a short time period is considered to be a spam activity. Bulk and automated following behaviors are used by spammers to garner unsolicited attention and artificially inflate follower counts, frequently due to the perception that users should follow-back. In addition to spam, this behavior often leads to unusable timelines and direct messages inboxes. To discourage these activities, automated and bulk unfollowing is also disallowed.
We understand that there are people and businesses who have good intentions when they bulk follow/unfollow and who aren’t looking to engage in spam activities.
However, to help us prevent spam and maintain a positive Twitter experience for users, we have disallowed all forms of this activity.”
Whilst we maintain that there is a superior approach to reducing spam that doesn’t have to eliminate bulk following/unfollowing entirely, it is reassuring to see that Twitter have noted that there are legitimate use cases for bulk following/unfollowing. Furthermore it is positive to see that twitter implicitly see the value of services to surface potential accounts to follow or unfollow.