Standard approaches to functional safety as described in the automotive functional safety standard ISO 26262 are focused on reducing the risk of hazards due to random hardware faults or systematic failures during design (e.g. software bugs). However, as vehicle systems become increasingly complex and ever more connected to the internet of things, a third source of hazard must be considered, that of intentional manipulation of the electrical/electronic control systems either via direct physical contact or via the systems' open interfaces. This article describes how the process prescribed by the ISO 26262 can be extended with methods from the domain of embedded security to protect the systems against this third source of hazard.