Seoul Metro reported a multi-month compromise of office PC management infrastructure for subway lines 1 through 4, affecting 58 infected PCs, abnormal access involving 213 PCs, and loss of control over PC management and webzine servers. Investigators said 12 internal business documents were exfiltrated and South Korea's National Intelligence Service assessed the activity as likely linked to North Korea's Reconnaissance General Bureau, while Seoul Metro stated the affected office systems were separated from train-control and signaling networks.