A method of validating a user, comprises the steps of:—storing for a user data representative of a validation code for the user comprising a combination of symbols selected from a set of symbols; presenting a displayed image including a plurality of designatable areas in which said set of symbols is distributed between said designatable areas such that each designatable area contains a plurality of said symbols; varying the image between subsequent presentations such that the distribution of said symbols between said designatable areas changes between subsequent presentations, validating a user in an validation routine by detecting designation by a user of a combination of said designatable areas in a presented image, and determining whether the combination of designated designatable areas contains the combination of symbols making up the validation code for said user.