There have been reports from people whose Macs have been locked remotely via Find My Mac, with the criminals responsible holding access to the Mac hostage until they receive a ransom in Bitcoin. First, if this happens to you, do not pay the ransom! Any Apple Authorized Service Provider (like MacLife) or Apple Store can unlock your Mac for you if you bring it in and provide proof of purchase. Second, if you ever used your iCloud password on another site, change it immediately, since if that site was hacked, your iCloud account is now vulnerable. Unfortunately, Apple’s two-factor authentication, which is otherwise great, does not currently protect against this problem.