Adversarial EXEmples are carefully-perturbed programs tailored to evade machine learning Windows malware detectors, with an on-going effort in developing robust models able to address detection effectiveness. However, even if robust models can prevent the majority of EXEmples, to maintain predictive power over time, models are fine-tuned to newer threats, leading either to partial updates or time-consuming retraining from scratch. Thus, even if the robustness against attacks is higher, the new models might suffer a regression in performance by misclassifying threats that were previously correctly detected. For these reasons, we study the trade-off between accuracy and regression when updating Windows malware detectors, by proposing EXE-scanner, a plugin that can be chained to existing detectors to promptly stop EXEmples without causing regression. We empirically show that previously-proposed hardening techniques suffer a regression of accuracy when updating non-robust models. On the contrary, we show that EXE-scanner exhibits comparable performance to robust models without regression of accuracy, and we show how to properly chain it after the base classifier to obtain the best performance without the need of costly retraining. To foster reproducibility, we openly release source code, along with the dataset of adversarial EXEmples based on state-of-the-art perturbation algorithms.

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