What is "winlogon"

In computing, Winlogon is the component of Microsoft Windows operating systems that is responsible for handling the secure attention sequence, loading the user profile on logon, and optionally locking the computer when a screensaver is running (requiring another authentication step). The actual obtainment and verification of user credentials is left to other components. Winlogon is a common target for several threats that could modify its function and memory usage. Increased memory usage for this process might indicate that it has been "hijacked". In Windows Vista and later operating systems, Winlogon's roles and responsibilities have changed significantly.