The cyber security company backed by extradited entrepreneur Mike Lynch is to be snapped up by a US private equity firm in a further blow for the London Stock Exchange. Darktrace, one of the UK’s biggest listed tech companies, has agreed a £4.2bn takeover by  Chicago-based Thoma Bravo. The deal will mean a significant payday for Mr Lynch, who is currently standing trial in the US for alleged fraud at Autonomy, another of the companies that he founded. Mr Lynch and his wife have a combined stake of around 7pc, meaning they are in line for almost £300m. Thoma Bravo has agreed to buy the business for $7.75 (620p) a share. Darktrace stock leapt almost 30pc on the news to 617p, in a sign the markets expect the takeover to go through. The deal comes less than two years after Thoma Bravo pulled out of talks to buy Darktrace and just three years after the company listed in London. Thoma Bravo said it would keep Darktrace’s Cambridge headquarters and its research operations in the UK. Announcing the deal, Darktrace said the company had been undervalued by public investors. It said: “The Darktrace Board believes that Darktrace’s operating and financial achievements have not been...