Max Vision has found a buffer overflow in Netscape 4.7 that can be used to crash the browser or possibly to execute arbitrary programs. The overflow occurs in the dynamic font feature which you can switch off to avoid this problem. Nice to see that it isn't just IE that's having all the problems. He's put a demo up on the web. The relevant code is linked from the demo page so it's safe to visit with Netscape 4.7.