When the FBI warns the public about a scam, you know it's serious. And that's the Phantom Hacker scam.
To make a long story short, the scam has 3 phases.
1) A random call from a major company (this is fake, BTW), such as Amazon, or a company you deal with) trying to convince you that you've been hacked, and they will convince you to download a remote control software so they can takeover your computer later. After convincing you, they hand off to part 2, a "fraud department of your financial institution".
2) A second fake contact calls you, claims to work for the fraud department of your bank, where they will help you *scan* for fake transactions, then tell you that your account is vulnerable, and they will "help" you move your money to some "safe place" operated by the Feds.
3) A third fake contact calls you, falsely claiming to work for the Feds, assures you your money will be fine and returned to you after they trace the hacker. Except there never was a hacker, and your money disappears and never seen again.
So what can you do? Do NOT believe random pop-ups or calls, no matter how urgent they appear to be. Most companies operate some sort of 24/7 helpline or chat channel online.
Beware the phantom hacker scam.