Cryptovirologies is an array of techniques using cryptography to hide viruses and malware.
According to this article McAfee discovered a new malware that use Microsoft Windows’ Encrypted File System to scramble its payload and evade detection.
The attack tool consists of two main components, a dialer known as Qdial-45 and an encrypted downloader known as Spy-Agent.bf. The dialer disconnects the current modem connection and then dials a premium service for displaying adult content. The downloader uses the Encrypted File System (EFS) to obfuscate itself and retrieves updated content from a list of sites on the Internet.