  Deep Neural Networks (DNN) are susceptible to backdoor attacks where
malicious attackers manipulate the model's predictions via data poisoning. It
is hence imperative to develop a strategy for training a clean model using a
potentially poisoned dataset. Previous training-time defense mechanisms
typically employ an one-time isolation process, often leading to suboptimal
isolation outcomes. In this study, we present a novel and efficacious defense
method, termed Progressive Isolation of Poisoned Data (PIPD), that
progressively isolates poisoned data to enhance the isolation accuracy and
mitigate the risk of benign samples being misclassified as poisoned ones. Once
the poisoned portion of the dataset has been identified, we introduce a
selective training process to train a clean model. Through the implementation
of these techniques, we ensure that the trained model manifests a significantly
diminished attack success rate against the poisoned data. Extensive experiments
on multiple benchmark datasets and DNN models, assessed against nine
state-of-the-art backdoor attacks, demonstrate the superior performance of our
PIPD method for backdoor defense. For instance, our PIPD achieves an average
True Positive Rate (TPR) of 99.95% and an average False Positive Rate (FPR) of
0.06% for diverse attacks over CIFAR-10 dataset, markedly surpassing the
performance of state-of-the-art methods.
