Ransomware is a malicious software that takes over a computer and locks the user out, preventing them from accessing any files until they pay money.

Windows users need to be notified ASAP of a new ransomware strain and take immediate measures to patch their systems. It may be one of the biggest recorded ransomware attacks ever, with tens of thousands of infected computers in nearly 100 countries.

Specifically, on May 12, 2017, a new strain of the Ransom.CryptXXX (WannaCry) ransomware began spreading widely. WannaCry asks for about $300, though the price increases over time.

Note three easily-to-implement precautions by CNN Tech:

1. Install any software updates immediately and make it a regular habit. Turn on auto-updater where available. If you have yet to install the Microsoft fix—MS17-010— you should do so immediately.
2. Install and keep Windows anti-virus software up-to-date.
3. Have a backup routine to regularly save copies of all your files. If your machine gets infected and your photos and documents are encrypted, you don’t need to worry about losing them.

Most importantly, always stay alert. Be extremely suspicious of all e-mails you receive, particularly those that ask the recipient to open attached documents or click on Web links. Don’t click on links that you don’t recognize, or download files from people you don’t know personally.

Note that it’s not just your computer that you need to be worried about. This attack has impacted many large services and organizations, including hospitals in England, a telecom and natural gas company in Spain, and FedEx. Basic services that impact your life could be affected even if your own machine is clean.