Cybersecurity firm Proofpoint announced Thursday that it will acquire German rival Huangsong Security for $1 billion to strengthen its European operations to explore returns to the public market.

The deal marks the largest acquisition in Proofpoint's history.

The Sunnyville, California-based company is currently owned by private equity giant Thoma Bravo, which says the deal to buy the Hornets will help deepen its expertise in the hosting provider (MSP) ecosystem.

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

ProofPoint CEO Sumit Dhawan told CNBC that the deal will help “merge fragmented security tools into a unified platform that protects people and defends data in a global threat environment.”

"The generated AI fundamentally changes the threat landscape, allowing faster, more targeted and more complex attacks to be faster," Dhawan said in an interview. He added that small and medium-sized companies are “increasingly in the crosshairs of hackers” and require “integrated, efficient” solutions.

Proofpoint's boss told CNBC last October that the company is exploring external funding and mergers and acquisitions of smaller cybersecurity companies with the aim of returning to the public market in 2026. The company privately acquired private equity firm Thoma Bravo for $12.3 billion in 2021.

"Hornetsecurity provides a very strong business for new markets targeting MSPs and diversifies our route to the market," Dhawan said.

He added: “This contributes a lot to our revenue and cash flows, which makes us a stronger company and business as we explore the returns in the public market.”

Dhawan said that although there are currently no "new" in Proofpoint's IPO program to share, "we are still interested in the IPO market and will explore the public market when we think the time is right."

According to the press release, Hornets serve more than 125,000 small and medium-sized businesses and have more than 700 employees. ProofPoint has over 4,500 employees and regards 85% of the Fortune 100 as a customer.

The transaction is expected to be completed in the second half of 2025, but customary end conditions are subject to compliance.