Mobile code technology is gaining growing importance for example for electronic commerce applications. To come to a widespread use of mobile agents a lot of security aspects have to be seriously considered and security problems have to be solved to convince potential users of this technology. So far, most work concerning security in the area of mobile code was done to protect hosts from malicious agents. However, in the very recent literature approaches are discussed which lead to different levels of security for the mobile agent against attacks by dishonest hosts. A central problem consists in the integrity of computation: In order to profit from mobile agent technology, techniques have to be used which guarantee the correctness of the results returned by a mobile agent to its originator. In this paper we explain a general approach to cope with the integrity problem by supplementing computation results with very short proofs of correctness which can a posteriori be checked by the originator of the mobile code to verify whether the result is reliable or not.