Opera is the only browser (among the big ones — Internet Explorer (IE), Firefox, and Safari) to have patched 100% of its known security bugs, according to Secunia, a site that tracks security vulnerabilities in various applications…

Browser patches between Feb 2003 and Jan 2007:

IE6 — 67% patched (out of 110 reported bugs).

IE7 — 25% patched (out of 4 reported bugs).

Firefox 1 — 87% patched (out of 39 reported bugs).

Firefox 2 — 50% patched (out of 4 reported bugs).

Opera 8 — 100% patched (out of 15 reported bugs).

Opera 9 — 100% patched (out of 3 reported bugs).

Safari 1 — 93% patched (out of 15 reported bugs).

Safari 2 — 33% patched (out of 6 reported bugs).