A 0-Day denial of service (DoS) vulnerability has been discovered by Pietro Oliva , a student of network security at the department of IT (University of Milan in crema) , which affects multiple Browsers across operating systems. Though Peter is keeping the exploit private for now, he has mentioned to us that the problem lies in the way the browsers handle javascript. 

According to him the latest version of the following browsers are affected: IE, Firefox, Safari, Konqueror, Galeon and Seamonkey. The detailed version numbers are mentioned in the video. The only ones immune seem to be Opera and Chrome. Pietro shows a demo of the DoS using each of the above browsers in the 2 videos embedded below.