iCloud account keeps getting locked
I only occasionally log into icloud.com via web browser -- usually I just use iCloud in the Mail app, Messages, etc.
Whenever I do log into icloud.com via browser, it always tells me that my account has been locked for security reasons, then it forces me to change my password.
This has happened again and again for a few months. I can't figure out what keeps triggering my account to be locked. Maybe there are just constant attempts to hack into my account. But... could something else be causing this?
MacBook Pro 14″