GMER - 372KB (Open Source)
GMER is a simple yet powerful anti-malware tool that thoroughly scans your system for vulnerabilities and evidence of Rootkit activity. It has a standard explorer interface with a tabbed toolbar comprising of Processes, Modules, Services, Files, Registry, Rootkit/Malware, CMD, and Autostart.
GMER scans for:
Not only does GMER scan for malware, it also allows you to monitor the following system functions: process creating, driver loading, library loading, file functions, registry entries, and TCP or IP connections. Overall, GMER is a specific tool that specializes in Rootkit removal. It is fast, relatively lightweight and does exactly what is says on the tin: a great anti-Rootkit remover.
*GMER runs only on Windows NT/W2K/XP/VISTA/7/8. Important: The developer has recommended downloading GMER with a different name to avoid detection by certain malware, which may prevent GMER from launching.