.Onion Ransomware Virus

.Onion is the new extension used by the Dharma ransomware virus. The .Onion virus aims to encrypt your files and demand ransom for their decryption.

The .Onion virus will be dropped into your computer, after which the virus will attempt to get itself deep into the operating folders. The usual folders are: The dropped files will try to mask themselves as other system files. The OS is full of such little files, so it may be hard to locate them if you’re trying to remove the virus. This is why manual removal can be tricky, if not outright dangerous for your system.
 * AppData.
 * Temp.
 * Roaming.
 * System32.
 * Common.

Source:
.Onion Dharma Ransomware Virus – Remove And Restore Your Windows