Sept 19 (Reuters) - Cybersecurity firm KnowBe4 Inc (KNBE.O) said on Monday that Vista Equity Partners had offered to take it private for $4.22 billion in cash, the latest sign of private equity interest in a sector whose valuations have declined in this year's downturn. The offer of $24 per share represents a premium of nearly 39% to KnowBe4's closing price on Sept. 16. Register now for FREE unlimited access to Reuters.com RegisterKnowBe4 provides security awareness training with simulated phishing attacks on its platform. KnowBe4, whose shares surged 25% in the morning hours on Monday, said it had formed a special committee to review the offer. The bid from Vista comes amid a string of large investments by the Austin, Texas-based fund this year.

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