A computing method includes running on a user computer a first operating environment for performing general-purpose operations and a second operating environment, which is configured expressly for interacting with a server in a communication session and is isolated from the first operating environment such that the general-purpose operations performed in the first operating environment do not affect operation of the second operating environment. The operation of the second operating environment running on the user computer is monitored by means of a central management subsystem, which is external to the server and to the user computer. The communication session is controlled based on the monitored operation.