Serverless computing is becoming increasingly relevant in the cloud and applied in other fields, such as telecom. This paper proposes the Moving Functions as a Service (MoFaaS) system, a Moving Target Defense (MTD) and N-Version Programming (NVP)-based approach designed to improve the protection of applications and services built using Function as a Service (FaaS). The mechanism works by rotating the version to be executed next for each function. Therefore, when an attacker triggers the execution of a specific workflow path in distinct moments, the versions of the functions responding to those requests will probably be different. Consequently, if one or more function variants are vulnerable, the attacker cannot target them reliably. In the end, we conducted a preliminary practical demonstration to prove this system's effectiveness. Its analysis shows that the attack difficulty increases with the number of versions per function and the versions an attacker has to compromise to achieve its objectives.