SystemDoctor, also known as an ErrorSafe clone, is a rogue registry cleaner that is designed to display pop-up or pop-under ads while you surf the web. SystemDoctor promises to fix errors in your system, but once installed onto your system it pops up exaggerated security threats to trick you into purchasing the SystemDoctor repair/maintenance application. SystemDoctor often comes bundled with other spyware and may be installed without your knowledge and permission. Since SystemDoctor installs its different variants on your hard disk, it may be difficult to remove it manually.