MSP cybersecurity news digest, May 26, 2025

## Executive summary A multi-item intelligence roundup reports an extended cyberattack-induced outage at Wisconsin wireless provider Cellcom, a CISA/FBI advisory and takedown regarding the Lumma stealer/C2 (millions of infections and hundreds of thousands of devices observed), SideWinder APT spear-phishing campaigns exploiting legacy Office CVEs to deliver StealerBot across South Asian ministries, a ransomware incident (Nefarious Mantis / Interlock cluster) causing system-wide outages at Kettering Health, and multi-year Chinese-linked campaigns deploying backdoors like MarsSnake, NanoSlate and HydroRShell against government and international targets.