Kaseya customers using the on-prem VSA server were affected by this attack. The threat actor, an affiliate of the REvil ransomware-as-a-service, identified and exploited a zero-day vulnerability. The vulnerability was exploited to introduce a malicious script to be sent to all computers managed by the server, therefore reaching all the end clients. This effectively reaches all managed clients. The script delivered the. REvil. ransomware and encrypted the systems encrypted. systems. The attack vector is no longer present, we published the details of the exploit in a follow-up technical post.”]