CompaniesOct 15 (Reuters) - Thoma Bravo-owned cybersecurity ​company Proofpoint will buy data ‌security firm Varonis Systems (VRNS.O), opens new tab in all-cash deal valued at about $6.3 billion, the ​companies said on Thursday.Under the ​agreement, Varonis shareholders will receive $49.75 ⁠per share in cash, representing ​a premium of 52% over Varonis' ​closing stock price on June 22, the day before initial speculation about a ​potential sale, according to the ​companies. Sign up here.Reuters ...