1. A method of protecting a computer system against potentially harmful activity of a privileged user authorized to perform sensitive computer system operations which non-privileged users of the computer system are not authorized to perform, the method comprising: deploying a risk agent in the computer system, the risk agent being communicatively coupled to a risk engine, the risk engine being operative in response to queries from the risk agent to perform rules-based risk assessments of activities identified in the queries and to provide responses conveying risk assessment results; and operating the risk agent in the computer system to: (a) identify a user as one of a privileged user and a non-privileged user, the privileged user being authorized to perform sensitive computer system operations the non-privileged user is not authorized to perform; (b) when the user is identified as the non-privileged user, refrain from performing a monitoring action that includes monitoring computer system activity of the user; (c) when the user is identified as the privileged user, then (i) perform the monitoring action to monitor computer system activity of the privileged user to detect initiation of a sensitive computer system operation, and (ii) identify the computer system operation as one of a sensitive computer system operation and a non-sensitive computer system operation, the sensitive computer system operation being either an unusual operation not normally performed by the privileged user or having special potential for causing disruption to a service provided by the computer system, the non-sensitive computer system operation normally being performed by the privileged user and lacking special potential for causing disruption to the service provided by the computer system; (d) when the computer system operation is identified as the non-sensitive computer system operation during the monitoring, then allow the computer system operation to proceed and refrain from performing an assessment to determine whether the computer system operation exceeds a predetermined criteria of riskiness; (e) when the computer system operation is identified as the sensitive computer system operation during the monitoring, then perform the assessment to determine whether the sensitive computer system operation exceeds the predetermined criteria of riskiness, and if not then (i) allow the sensitive computer system operation to proceed and (ii) refrain from performing an additional security related processing; and (f) when the sensitive computer system operation is determined to exceed the predetermined criteria of riskiness, then perform the additional security related processing by: (1) formulating and sending a query to the risk engine requesting risk assessment for the sensitive computer system operation, (2) receiving a response to the query from the risk engine, and (3) based on a risk assessment result in the response, selecting one of a set of control actions and performing the selected control action, the set of control actions including allowing the sensitive computer system operation to proceed, preventing the sensitive computer system operation from proceeding, issuing a notification that the sensitive computer operation is proceeding, and obtaining further confirmation as a condition to allowing the sensitive computer system operation to proceed.