When did Leslie Nielsen become CISO of Mimecast?

The appointment was announced in the week of September 1, 2025, per SecurityWeek Industry Moves. The record holds the announcement, not a start date.

Where did Leslie Nielsen work before Mimecast?

Before the appointment, Leslie Nielsen was SVP and CISO at Klaviyo, according to the announcement (SecurityWeek Industry Moves).

Executive record

Leslie Nielsen

Career profile: Leslie Nielsen on CISO Spotlights ↗

Leslie Nielsen is Chief Information Security Officer at Mimecast. The appointment was announced in the week of September 1, 2025, per SecurityWeek Industry Moves.

Before the appointment: SVP and CISO at Klaviyo, per the same source.

1 tracked move on the Wire · Updated November 10, 2026

Career timeline

Every move the record holds for Leslie Nielsen, newest first, with the earlier roles the announcements name.

week of September 1, 2025· Appointment
Named Chief Information Security Officer at Mimecast
Source: SecurityWeek Industry Moves (week of 2025-09-01) ↗ · Move record
Before September 2025· Earlier role
SVP and CISO at Klaviyo
Named in the announcement of the Mimecast appointment · Source: SecurityWeek Industry Moves (week of 2025-09-01) ↗

The appointment

Announced week of September 1, 2025 · Source: SecurityWeek Industry Moves (week of 2025-09-01) ↗ · Move record

Leslie Nielsen has joined Mimecast as Chief Information Security Officer, coming from Klaviyo where he served as SVP and CISO. Prior to Klaviyo, Nielsen held SVP and CISO roles at Nuance Communications, SAP Concur, and SuccessFactors.

According to the release, Nielsen will lead the global cybersecurity strategy at Mimecast, covering threat intelligence, incident response and risk assessment initiatives. The release says Nielsen will also be responsible for ensuring regulatory compliance at Mimecast, which serves more than 42,000 global customers.

The release says Nielsen has spent more than 25 years in cybersecurity and describes Klaviyo as a marketing automation platform. Before Klaviyo, he was CTO at SOS Security and held senior roles at IBM and at ACS, which Xerox acquired, the release says. He has also served on Google's CISO Cloud Advisory Board, according to the release. The release says Nielsen studied Computer Science at Texas Tech University, where he earned a Bachelor of Science.

In the release, Nielsen said he was joining Mimecast on its mission to secure the human layer in a new age of AI-powered threats. According to the release, Mimecast's connected human risk platform is AI-powered and API-enabled and is built to protect organizations from a spectrum of cyber threats.

The company: Mimecast

Sector: Cybersecurity Vendors
Region: North America
Company record: Who runs security at Mimecast: 1 confirmed move on the record
Vendor directory: Mimecast sells security products, filed under Email security. What it sells

In their own words

What Leslie Nielsen has posted and written in public while in the seat, each described in our words with a link to the original. A post loads from LinkedIn or X only when you choose Show post. All voices

Talks and interviews

Conference sessions, podcast episodes and videos with Leslie Nielsen that the record holds, each from the event or the show's own page. The speaking circuit · Podcasts

August 26, 2026· Podcast appearance, Business Security Weekly (Audio)
Leslie Nielsen, Chief Information Security Officer at Mimecast
Connecting Cyber Risks to Board Outcomes & BHUSA interviews from Mimecast & Zscaler - Leslie Nielsen, Brett Stone-Gross, Dan Bowden - BSW #462
On linking cyber risk management to board-level decision outcomes
Our take
The CISO of Mimecast, in the seat since the announcement in September 2025, arrived from SVP and CISO at Klaviyo. The episode covers connecting cyber risk to board outcomes, with a guest discussing ransomware as extortion and data theft, third-party and cloud dependencies, and claims research, alongside conference interviews on agentic AI as human risk and on ransomware targeting managers. Our view on the board thread: translating cyber into resilience, financial exposure, regulatory impact and reputation is the right frame, but it only works if the numbers behind it are ones the CFO would also use, so build scenarios with finance and the risk function before the board meeting, not in it. We would add that dependency-driven interruption deserves its own line in board reporting, because outages that start at a supplier or cloud provider rarely show up in a control-maturity score. On agents as an extension of human risk, we agree in practice: giving each agent a named owner, scoped access and the same lifecycle controls as a person is a faster start than waiting for a new product category. Where we would push further is accountability, since an agent holding a human's credentials makes the deploying employee's access review the real control point. Watch whether boards begin asking for agent inventories the way they now ask about third parties.
Listen at Business Security Weekly (Audio) ↗
January 6, 2026· Podcast appearance, CISO Series Podcast
Leslie Nielsen, Chief Information Security Officer at Mimecast
Imagine Scaling Mistakes 5x Faster. Thank You, Automation! (LIVE in NY)
On automation amplifying security scaling mistakes
Our take
The CISO of Mimecast, in the seat since September and previously SVP and CISO at Klaviyo, joined a live CISO Series Podcast recording in New York. The episode covers automating dysfunction, leading without dominating, unglamorous wins and code without comprehension. We read the first topic as the one that matters most to programmes this year: automation does not repair a process, it repeats it at speed, so a muddled triage queue or a vague ownership model simply produces bad outcomes faster and in greater volume. Our advice is to document the manual workflow, name its owner and set a measure of what good looks like before any tooling is added, and to keep a human checkpoint on steps that touch access or customer data until the output has earned trust. Code without comprehension deserves the same discipline now that generated code reaches production quickly, because a team that cannot explain what shipped cannot defend or patch it. Reviewers should be able to state what a change does and why, not merely that tests passed. The unglamorous wins theme is a useful counterweight, since boring fixes such as asset inventory and clean offboarding usually pay back more than a new platform, and they are the processes worth getting right before anything is automated. Watch whether boards begin asking for the process behind an automation rather than the headline gain from it.
Listen at CISO Series Podcast ↗

Elsewhere

Public profiles we matched to Leslie Nielsen by exact name and the company on our record. Links only; we do not copy from them.

LinkedIn ↗

Appointed in the same period

Other security chiefs in Cybersecurity Vendors whose appointment was announced within 90 days of Leslie Nielsen's, nearest first. The Cybersecurity Vendors bench

August 19, 2025
Aman Sirohi, Chief Information Security Officer at Cyberhaven
week of August 18, 2025
Olivia Brännlund, CISO at Outpost24
week of August 4, 2025
Diana Kelley, Chief Information Security Officer (CISO) at Noma Security
week of July 28, 2025
Quincy Castro, Chief Information Security Officer (CISO) at Chainguard
week of October 13, 2025
Raj Umadas, Chief Information Security Officer (CISO) at RAD Security
July 8, 2025
Dale Hoak, Chief Information Security Officer at RegScale
week of November 24, 2025
John Bruce, Chief Information Security Officer at Quorum Cyber
week of June 9, 2025
Rinki Sethi, Chief Security Officer (CSO) at Upwind

Record facts

Time in the seat: About 1 year 2 months since the appointment was announced (week of September 1, 2025), as of November 2026
Moves on the record: 1 confirmed move, each with its source
On the record since: September 26, 2026
Cybersecurity Vendors in 2026: 25 security-leadership appointments announced in the sector on the record

How these are counted. Time in the seat: Counted in whole months from the announcement of the appointment, the date the record holds; announcements rarely give a start date.

Questions about Leslie Nielsen

Who is the CISO of Mimecast?: Leslie Nielsen is Chief Information Security Officer at Mimecast. The appointment was announced in the week of September 1, 2025, per SecurityWeek Industry Moves.
When did Leslie Nielsen become CISO of Mimecast?: The appointment was announced in the week of September 1, 2025, per SecurityWeek Industry Moves. The record holds the announcement, not a start date.
Where did Leslie Nielsen work before Mimecast?: Before the appointment, Leslie Nielsen was SVP and CISO at Klaviyo, according to the announcement (SecurityWeek Industry Moves).

Sources

1.SecurityWeek Industry Moves (week of 2025-09-01) ↗: the appointment at Mimecast, week of September 1, 2025
2.CISO Spotlights career profile ↗: a fuller career profile on a sister site

This record begins with CISO Tribune's tracking in 2026.

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