About two weeks ago I received a notification from Dropbox that somebody signed in that I did not recognize. I immediately changed my password and enabled 2FA. There were no open unknown sessions or any activity that seemed suspicious other than that one login.
One odd thing at the time: the Dropbox login page had started offering 'Continue with SSO' for my email even though I never created a Lenovo ID.
Another submission on HN (to Twitter).