WHY are there thousands of new ancestors added to my tree by other users?

I've worked so hard on keeping my tree organized and only containing the exact information I want in the format I want, and now suddenly as of today, there are thousands of new ancestors added to my tree by other users!!  How is this possible when my account and tree are set to private?  I REALLY don't want all this extra stuff on here confusing and clogging up everything!  Is there any way to only view the entries that I've added to my tree myself??  I feel like my tree and all that hard work is basically ruined now.