The traffic caused by these distributed spam attacks is currently causing federation delays for servers which are participating in a targeted room; we are working on a performance fix for Synapse to address this.
@matrix Meanwhile server admins can use delete room API to remove users from Matrix HQ and remove it's data until things settle down. Documentation for the API is at https://github.com/matrix-org/synapse/blob/develop/docs/admin_api/rooms.md#delete-room-api and Room ID for HQ is !OGEhHVWSdvArJzumhm:matrix.org
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