Cybersecurity firm Proofpoint announced Thursday it will acquire Germany-based competitor Hornetsecurity for $1 billion to strengthen its European presence as it explores a return to public markets.

The deal marks the largest single acquisition in Proofpoint’s history.

The Sunnyvale, California-based company, which is currently owned by private equity giant Thoma Bravo, said the deal to buy Hornetsecurity would help deepen its expertise in the managed service provider (MSP) ecosystem.

Headquartered in Hannover, Germany, Hornetsecurity specializes in managed cloud-based email security services to help protect firms from cyberattacks, data loss, and compliance risks associated with Microsoft 365 and other IT infrastructure.

Proofpoint CEO Sumit Dhawan told CNBC the deal will help “consolidate fragmented security tools into a unified platform that protects people and defends data across the global threat landscape.”

“Generative AI has fundamentally changed the threat landscape, enabling faster, more targeted, and more complex attacks,” Dhawan said in an interview. Small and medium-sized firms “are increasingly in the crosshairs” of hackers and require “integrated, high-efficacy” solutions, he added.

Proofpoint’s boss told CNBC in October last year that the company was exploring external funding as well as mergers and acquisitions of smaller cybersecurity firms with an aim to return to the public markets in 2026. The company went private in 2021 in a $12.3 billion acquisition by private equity firm Thoma Bravo.

“Hornetsecurity brings very strong business to Proofpoint targeting a new market segment of MSPs and diversifies our routes to market,” Dhawan said.

“It contributes significantly to our earnings and cash flow going forward, which makes us an even stronger company and business as we explore a return to public markets,” he added.

Dhawan said that while there is “nothing new” to share on Proofpoint’s IPO plans for now, “we remain interested in the IPO market and will explore public markets when we feel the time is right.”

Hornetsecurity serves more than 125,000 small to medium-sized businesses and has more than 700 employees, according to a press release. Proofpoint has over 4,500 employees and counts 85% of the Fortune 100 as customers.

The deal is expected to close in the second half of 2025, subject to customary closing conditions.