Researchers at Avast Threat Labs spent time looking at a specific part that malware authors use to make their cars A crypter is a tool used to hide malicious parts of code using encryption. Malware authors use this technique to hide their malicious code from researchers, antivirus and security software. In the last three years, we have protected almost 400,000 Avast users around the world from malware that makes use of OnionCrypter. In advertising on forums, this is frequently advertised as a fully undetectable (FUD) crypter.”]
Source: https://blog.avast.com/onioncrypter-threat-research-avast