Warren Buffett, the 94-year-old CEO of Berkshire Hathaway.Daniel Zuchnik / Getty ImagesBerkshire 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.Warren Buffett's Berkshire Hathaway is buying up shares of internet domain services provider VeriSign.A Form 4 filing with the Securities and Exchange Commission on Thursday revealed Berkshire Hathaway's latest acquisition of 143,424 shares in the three trading sessions that ended December 24.