Microsoft recently informed us that a Mimecast-issued certificate provided to certain customers to authenticate Mimecast Sync and Recover, Continuity Monitor, and IEP products to Microsoft 365 exchange web Services has been compromised by a sophisticated threat actor.
Approximately 10 percent of our customers apply this connection. Of those that do, there are indications that a low single digit number of our customers M365 tenants were targeted. We have already contacted these customers to remediate the issue.
As a precaution, we are asking the subset of Mimecast customers using this certificate-based connection to immediately delete the existing connecter within their M365 tenant and re-establish a new certificate-based connecter using the new certification weve made available. Taking this litigate does not impact inbound or outbound mail flow or associated certificate scanning.
The security of our customers is always our cover priority. We have engaged a third-party forensics expert to assist in our investigation, and we will work closely with Microsoft and law enforcement as appropriate.