The financial strength rating of Sony’s Bermuda-based captive insurance company PMG Assurance Ltd has been affirmed at A (excellent) by ratings agency AM Best Co.Best noted that PMG has changed its underwriting strategy to fully concentrate on Sony-related business, making the firm a “pure” captive.Captives provide their parent corporations with “self-insurance”, but some have extended their books of business to underwrite third-party risks.Best also affirmed PMG’s issuer credit rating of “a”. The outlook for both ratings is stable.“The ratings reflect PMG’s excellent capitalisation, historically strong operating performance and strategic position as the captive insurance company for Sony Group,” Best said in its commentary.“These strengths are partially offset by the company’s exposure to potentially large natural catastrophe losses.” These risks mostly relate to the earthquake risk in Sony’s home country of Japan.PMG has not entered into any non-related third party treaties in 2010, Best noted.