i encounter sites that are blocked by the hostsfiles more than the ones that are blocked by the immunizers, and i am not counting the adservers in that ,because they i encounter often, but if you are talking about that sites that are blocked by ie-spyad then that is another case, because it is outdated, and the ones that i encounter the most which is blocked are innocent looking sites, and that is often. the hostsfiles i have used has also worked when i have used firefox, but i dont know how it works on others computers.