Buffett's Berkshire Hathaway bought 143,424 shares of VeriSign, an Internet infrastructure services company, for $28.55 million in the three trading days ending on the 24th, according to the latest filings. With previous purchases, Berkshire now owns 13.7% of VeriSign's issued shares, worth nearly $2.70 billion. According to reports, one reason for Buffett's interest in VeriSign may be that it ranks highly in various profit margin indicators of companies in the S & P 500 Index.