Heads up, Creators: On Dec 13-14 you may see a noticeable decrease in your sub count as we remove spam subscriptions. If spam is removed, you'll see a YouTube Studio alert: https://goo.gl/qGDBvX This should help give you confidence that the subs you do have are real fans!
We use technology to identify spam accounts and we don't remove legit subscribers from the sub count. For example, if you're subscribed to a channel and you haven't watched in a while, you'll still be subscribed. This update only removes spam accounts.