Ransomware is back in the news with a vengeance. The largest coordinated attack in history is underway, exploiting a vulnerability in Windows, and holding people’s computers hostage.

Ransomware infects your computer and encrypts your data. It demands payment before releasing it. Authorities have said repeatedly there’s not much you can do. If you pay the ransom, you aren’t likely to get your data back. If you don’t, there’s almost no way to retrieve it. It’s a lose-lose deal.

The best bet is prevention.

Microsoft found the vulnerability back in April and has made the update available for free. If you’re computer is set to automatically download and install updates, you should be fine. If you haven’t done it yet, do it now.

Online security firm Avast reports the attacks have been seen in more than 100 countries, including the United States. It’s estimated to have infected more than 200,000 computers.