Spa: Stealthy and Persistent Backdoor Attacks in Federated Learning via Feature-Space Alignment

Researchers discovered a new backdoor attack called Spa that can secretly compromise federated learning systems (distributed AI systems where multiple parties train a model together while keeping their data private). Unlike previous attacks, Spa hides malicious code by blending it with the legitimate learning process and uses adaptive triggers that change over time to avoid detection and remain effective for hundreds of training rounds.