Earlier this week, we wrote about a recent twist in so-called scareware schemes, where scammers send alarming messages to try to convince you that your computer is infected with viruses or other malware. Then, they try to sell you software to fix the problem. At best, the software is worthless or available elsewhere for free. At worst, it could be malware — software designed to give criminals access to your computer and your personal information.

The newest version of the scam begins with a phone call. Scammers call and claim to be computer techs associated with well-known companies like Microsoft. They say that they’ve detected viruses or other malware on your computer to trick you into giving them remote access or paying for software you don’t need.

So, what should you do if you get one of these calls?

Hang up. Legitimate companies won’t call you out of the blue and ask you to pay for tech support. If you’re concerned about your computer, call your security software company yourself on a phone number you know to be genuine.

What should you do if you’ve already responded to one of these scams?

Change any passwords that you gave out. If you use these passwords for other accounts, change those accounts, too.

If you paid for bogus services with a credit card, call your credit card provider and ask to reverse the charges. Check your statements for any other charges you didn’t make, and ask to reverse those, too.

And file a complaint with the FTC at ftc.gov/complaint.

Finally, what should you do if you suspect your computer has been infected with malware?

Stop shopping, banking, and doing other online activities that involve user names, passwords, or other sensitive information.

Update your security software, and then scan your computer. Delete anything it identifies as a problem. You may have to restart your computer for the changes to take effect.

If you can’t fix the problem on your own, your computer manufacturer or internet service provider may offer free tech support. If not, contact one of the many companies that offer tech support for a fee.

Once your computer is back up and running, think about how malware could have been downloaded to your machine, and what you could do differently to avoid it in the future.