From the Geoedge link:
Security:It sounds like Javascript in HTML5 can be exploited, but overall HTML5 is still safer than Flash.
Flash vulnerabilities allow for malicious software to install on a users computer silently. Currently, HTML5 has no vulnerability that would allow malicious software to install on a users computer silently. HTML5 alerts the user whenever an install attempt is made.
Also, DON'T CLICK ON POPUPS!
What about pop-overs and unders? Those are all I have problems with.