https://www.bleepingcomputer.com/news/security/microsoft-warns-of-surge-in-html-smuggling-phishing-attacks/

Microsoft has seen a surge in malware campaigns using HTML smuggling to distribute banking malware and remote access trojans (RAT).

While HTML smuggling is not a new technique, Microsoft is seeing it increasingly used by threat actors to evade detection, including the Nobelium hacking group behind the SolarWinds attacks.