In a report NSS Labs said that with a unique URL blocking score of 94 per cent and over-time protection rating of 99 per cent, Internet Explorer 9 was by far the best at protecting users against socially-engineered malware.” Internet Explorer 9 leads all browsers with the highest block rate - and best protection against malware. The main line of defence in IE9 is SmartScreen technology which was first seen in Internet Explorer 8. It protects by detecting and blocking websites that distribute socially-engineered malware and phishing attacks.
However in IE9, Microsoft beefed things up by code called SmartScreen Application Reputation. This adds an additional layer of protection by warning users when they attempt to download a higher risk application. Of course spotting Malware is not the only thing a browser should do.
Most of Microsoft's security flaws are found once the browser is put under pressure in the wild. Since that does not happen until a few months after its release we do not know if IE9 will be the most secure to date.