South Korea's top four accountancy firms virtually monopolized external audit services for the country's top 10 conglomerates last year, data showed Wednesday. Of the 83 firms affiliated with the top 10 business groups, 80, or 96.4 percent, appointed the four players -- Samil PwC, Samjong KPMG, Hanyoung Ernst & Young and Deloitte Anjin -- as their external auditors in 2013, according to the regulatory filings.