Its first act upon its arrival — or, depending on the degree of intelligent agency you ascribed to it, the first side-effect of its arrival — was the neutralisation of the Foundation. In the space of a night, an international staff of tens of thousands disappeared into oblivion, or became amnesiac, or simply dropped brain-dead where they were standing. Foundation Sites became hollow, inaccessible dead zones. A few anomalies broke containment in the chaos, to devastating effect; thousands of others were choked into irrelevant obscurity beneath SCP-3125's antimemetic pressure.
Source: wiktionary