You let a scammer connect to your computer
You're not the first, and acting in the next hour matters most. Disconnect first, then protect your money, then your passwords.
What's usually going on
The caller said they were from Microsoft, Apple, your bank, or a refund department, and asked you to install a program so they could "help". That program let them see and control your computer. They may have looked at your files, opened your bank, or left a way to get back in.
Worth trying first
Disconnect the computer.
Turn off Wi-Fi or unplug the network cable, then shut the computer down. That ends their connection. Don't answer if they call back.
Call your bank.
Use the number on the back of your card, not one they gave you. Tell the bank someone had access to your computer, and ask them to check for transfers and watch the account.
Change passwords from another device.
Use a phone or a different computer. Start with your email, then banking, then anything saved in the browser on the affected computer.
Remove the program they installed.
Remote tools such as AnyDesk, TeamViewer, or UltraViewer are legitimate programs used dishonestly. Uninstall any you didn't set up, then run a full scan with your built-in protection.
Report it.
In the US, report it to the FTC at reportfraud.ftc.gov. Your bank may also ask for a police report.
When to hand it over
Straight away, ideally before you turn the computer back on. We'll check what was installed and changed, remove it, and go through every account the computer could reach. Sometimes the only safe answer is to erase the computer and set it up again; if so, we'll keep your files.
Your own technologist, on call.
Tell us a little about your setup. We'll take it from there.