Last up among Berkshire Hathaway's conviction buys for the second quarter is VeriSign ( VRSN). 2013 has been a strong year for the $7 billion tech firm -- shares have rallied more than 25% since the calendar flipped over to January. And Buffett's team thinks that that uptrend is inclined to continue. That was reason enough to pick up 2.7 million shares of the firm, a 33% bump in their stake. >>4 Big Tech Stocks on Traders' Radars VeriSign is one of the biggest Internet infrastructure firms in the world, maintaining a central directory of all domains and many of the systems that run them. In a nutshell, VRSN's business is the Internet. The company is the gatekeeper to owning a .com Web address, and as a result, VeriSign is able to collect a fee for each of the more than 110 million domains that fall under its purview. VRSN's exclusive contract with ICANN gives it a legal monopoly on the domains under its control. As a result, it's got one heck of an economic moat. That moat became slightly shallower when the Department of Commerce decided that it would have authority to approve any price hikes for VeriSign's services, ending an era of automatic revenue bumps. But it doesn't change VRSN's attractiveness right now. This firm still owns a critical (and lucrative) part of the web infrastructure in 2013. To see the rest of Berkshire Hathaway's plays -- including a complete list of which stocks the firm added or sold off, check out the Warren Buffett Portfolio on Stockpickr. -- Written by Jonas Elmerraji in Baltimore.