"We believe that as a private company, we can be even more agile with greater flexibility to continue investing in innovation, building on our leadership position and staying ahead of threat actors," said chairman and CEO of Proofpoint Gary Steele. "Thoma Bravo is an experienced software investor, providing capital and strategic support to technology organisations, and our partnership will accelerate Proofpoint's growth and scale at an even faster pace. "This is an exciting new chapter for Proofpoint that would not have been possible without our employees' hard work and commitment to our customers, partners and each other." Proofpoint's valuation at $12.3bn dwarfs those of Symantec and McAfee, which both sold up to larger rivals or private equity for mouth-watering sums of money.