Darktrace, a cybersecurity specialist, is aiming to list at a reputed valuation of $5 billion. The company was co-founded by Mike Lynch, the software entrepreneur who is battling an American extradition request over alleged accounting fraud at Autonomy, the former FTSE 100 developer. He denies the charges. Darktrace's initial public offering has been complicated by its association with Lynch, whose fund owns about 30 per cent of the business.