Mimecast on August 27, 2025 announced that Leslie Nielsen has joined the company as Chief Information Security Officer (CISO). Nielsen is a 25+ year cybersecurity veteran who joins Mimecast from Klaviyo, where he served as SVP and CISO. At Klaviyo, he played a critical role in scaling the company to $1.3 billion in revenue, fortifying its defenses and leading its security function through IPO readiness, positioning the organization to meet the rigorous demands of the public markets.
As CISO, Nielsen will spearhead Mimecast?s global cybersecurity strategy, driving the company?s threat intelligence, risk assessment, incident response initiatives, as well as ensuring regulatory compliance, reinforcing Mimecast?s commitment to providing the highest levels of protection for its more than 42,000 global customers. Prior to Klaviyo, Nielsen held SVP and CISO roles at Nuance Communications, SAP Concur and SuccessFactors and the CTO role at SOS Security, along with senior roles at IBM and ACS (acquired by Xerox). He also was a member of Google?s CISO Cloud Advisory Board.
He earned his Bachelor of Science in Computer Science from Texas Tech University.
