  With the rapid development of sixth-generation (6G) communication technology,
global communication networks are moving towards the goal of comprehensive and
seamless coverage. In particular, low earth orbit (LEO) satellites have become
a critical component of satellite communication networks. The emergence of LEO
satellites has brought about new computational resources known as the
\textit{LEO satellite edge}, enabling ground users (GU) to offload computing
tasks to the resource-rich LEO satellite edge. However, existing LEO satellite
computational offloading solutions primarily focus on optimizing system
performance, neglecting the potential issue of malicious satellite attacks
during task offloading. In this paper, we propose the deployment of LEO
satellite edge in an integrated satellite-terrestrial networks (ISTN) structure
to support \textit{security-sensitive computing task offloading}. We model the
task allocation and offloading order problem as a joint optimization problem to
minimize task offloading delay, energy consumption, and the number of attacks
while satisfying reliability constraints. To achieve this objective, we model
the task offloading process as a Markov decision process (MDP) and propose a
security-sensitive task offloading strategy optimization algorithm based on
proximal policy optimization (PPO). Experimental results demonstrate that our
algorithm significantly outperforms other benchmark methods in terms of
performance.
