Windows Internet Explorer 8 (IE8) is a web browser developed by Microsoft in the Internet Explorer browser series, released on March 19, 2009. It is the successor to Internet Explorer 7, released in 2006, and is the default browser for Windows 7 and Windows Server 2008 R2 operating systems. Internet Explorer 8 is the first version of IE to pass the Acid2 test, and the last of the major browsers to do so, although it scores 24/100 on the Acid3 Test. According to Microsoft, security, ease of use, and improvements in RSS, CSS, and Ajax support were its priorities for IE8.