Most of the major social and email providers have optional two-factor authentication. If you aren't familiar with two-factor authentication, this means that every time you sign in you'll be sent a code via text message to verify your identity. You are able to whitelist devices, so you won't be bugged every time you log in on your phone or your computer, but every time you sign in on a new device it will force verification. This is a good way to find out quickly if someone is trying to use your account.