This looks like the prompt for a program whose menu item has been changed so that it has "run as administrator" enabled.
Assuming your task manager has the default setting of grouping by type, is it showing there as a 'background process" or does it show there with 'service' as part of the description?
If the program is set to begin by being minimized to tray, and the icon is being hidden due to being inactive, the mirc tray icon may be hidden inside the notification area where inactive icons are hidden. If that's happening, the mirc icon should be in the "background processes" section of the list of processes.
