Think an account has been hacked
Act quickly and in order. The email account comes first, because it is the key to all the others.
What's usually going on
Most break-ins start with a reused password or a convincing fake sign-in page. Once someone is in your email, they can reset the password on almost everything else. So that is where to start, even if the problem first showed up somewhere else.
Worth trying first
Use a device you trust.
Do everything below from a phone or computer you believe is clean, not the one where things looked strange.
Change the email password first.
Choose a new password you have never used anywhere else. Then do the same for banking and anything else that matters.
Sign out everywhere.
In the account's security settings, find the list of devices or sessions and sign out of all of them. That removes anyone who is still inside.
Check what they changed.
Look at the recovery phone number and email address, and at mail forwarding and rules. Intruders often add their own, so they can get back in or quietly receive copies of your mail.
Turn on two-step sign-in.
With a code from your phone required as well as the password, a stolen password alone is no longer enough.
When to hand it over
If you can't get back in at all, if money has moved, or if you'd rather someone went through every account properly. If money or bank details are involved, call your bank first using the number on your card, then get in touch.
Your own technologist, on call.
Tell us a little about your setup. We'll take it from there.