The scam starts with a pop-up labeled as a critical update from Microsoft. Once a user decides to apply the fake update, it extracts files and executes an embedded program called WindowsUpdate.exe... As with other EDA2 ransomware, Fantom generates a random AES-128 key, encrypts it using RSA, and then uploads it to the culprit. From there, Fantom targets specific file extensions and encrypts those files using AES-128 encryption... Users affected by this are instructed to email the culprit for payment instructions.
While the ransomware is busy encrypting your files, it displays Microsoft's standard warning about not turning off the computer while the "update" is in progress. Pressing Ctrl+F4 closes that window, according to the article, "but that doesn't stop the ransomware from encrypting files in the background."