A substantially burglary-proof lock, comprises a housing formed with a cylindrical bore defining an inner cylindrical surface, and a cylinder within said bore carrying locking elements movable to locking and unlocking positions with respect to said housing, said cylinder having an outer diameter equal to the diameter of said bore so as to be rotatable when the locking elements are in unlocking position with respect to said housing, said cylinder being formed with a keyway for receiving a proper key in order to move said locking elements to their locking and unlocking positions with respect to said housing, characterized in that said cylinder carries at least one insert of a hard material configured, dimensioned and located such as to prevent pull-out of the cylinder from the housing by a pull-out force applied to the cylinder, and/or by drilling through the locking elements.