Trojan:Win32/FakeSysdef, originally dispersed as an application called "HDD Defragmenter" hence the name "FakeSysdef" or "Fake System Defragmenter", is a Computer Trojan type of computer virus targeting the Microsoft Windows operating system that was first documented in late 2010. The branding strategy may look legitimate to computer users as the names are usually a combination of technical words such as "HDD", "Disk", "Memory" and action words such as "Scanner", "Defragmenter", "Diagnostics", "Repair", and "Fix".