1. A computer security method comprising: loading a software application from a non-volatile memory into a volatile memory of a computer system by a secure loader, where the software application is associated with characteristic information and where the characteristic information includes a pre-execution characteristic value of the software application; performing a first authentication of the software application; starting execution of the software application after the first authentication; and performing a second authentication of the software application during the execution comprising: calculating an execution characteristic value of a runtime image of the software application; and determining if the pre-execution characteristic value and the execution characteristic value match.