TDL4 is encrypted using custom algorithms and will stay hidden on the system after it has successfully infected your system. The rootkit can infect both 32- and 64-bit versions of Windows, which makes it particularly more dangerous than other pieces of malware based in accompanied by drivers. The piece of malware (which has been around since 2008 and suffered four major upgrades) spreads through pornography websites, as well as through illegal file sharing repositories, where it is disguised as cracks or codecs. BitDefender has added detection, removal and disinfection in its antimalware solutions.”]
Source: https://www.bitdefender.com/blog/hotforsecurity/free-removal-tool-for-tdl4-available-now/