Renaissance Technologies, which investors have described as the best computer-driven hedge fund manager, has revealed its $27bn (€20bn) institutional fund lost 8.7% in the first eight business days of August, thought to be its worst loss since 1989.

Jim Simons, the founder of the firm, which employs dozens of PhD-qualified staff to modify and attune a computer model that makes investment decisions, said in a letter at the end of last week the losses had arisen through other hedge funds liquidating their positions.