It seems the possibility you have been hacked is quite high. As the Twitter Help Center Page states, here are some common things that happen when you are hacked:
Noticed unexpected Tweets by your account
Seen unintended direct messages (DMs) sent from your account
Observed other account behaviors you didn't make or approve (like following, ...
Here you go:
Yes, when you follow a public figure or a non-friend, a notification will be send to them.
No, unfollowing or re-following any friend will not send notification to that person.
Check these links to understand about follow and unfollow:
What does it mean to follow someone or a Page?
How do I follow or unfollow a profile or Page?
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Slack does not have a build-in "follow" feature. If you need this feature I would advise to send a mail to the Slack team. They are very helpful and are open to add new features based on user input. One straightforward way to implement this for the Slack team would be to add users to notification settings, similar to keywords.
Or you can implement it with ...
Go to Activity Log in your facebook account and then use the Filter option and filter by "Following". Hopefully it will show you the list of people you followed. I have tried this in the facebook android app, should be the same feature in other platform apps and also browser.
Go to apps in the settings,
You can't directly identify which. What you can do:
You have to check for the apps with permission write, only these apps can manipulate your account in this regard.
Also use the browser find to search the word follower in the apps section, if you are lucky the apps which do this thing use the word follow or follower somewhere ...