Warren Buffett's Berkshire Hathaway is buying up shares of internet domain provider VeriSign.Berkshire Hathaway increased its stake in VeriSign to $2.7 billion, becoming its largest shareholder.VeriSign, founded in 1995, is known for its high profit margin and ranks fifth in the S&P 500.VeriSign stock is down 2% year-to-date, completely sitting out the broader stock market rally.