The latest documents show that Berkshire Hathaway, led by Buffett, increased its stake by $28.55 million to purchase 143,424 shares of internet infrastructure service company VeriSign over three trading days ending on the 24th. Including previously acquired shares, Berkshire now holds 13.7% of VeriSign's outstanding shares, valued at nearly $2.7 billion. Reports suggest that one reason Buffett is interested in VeriSign could be its high rankings in various profitability metrics among the companies in the S&P 500 index.