Trojan:Win32/FakeSysdef, originally dispersed as an application called "HDD Defragmenter" hence the name "FakeSysdef" or "Fake System Defragmenter", is a Trojan 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".