A condition announced by the US Cybersecurity and Infrastructure Security Agency (CISA) to draw attention to a temporary period of high alert, associated with expectation of a connected wave of cyberattacks prompted by either a widespread vulnerability or an unusually active and capable threat actor. A CISA Shields Up announcement is meant to prompt organizations to enhance their security and resiliency by applying well-established best practices; CISA offers appropriate advice on the best practices.