Disallowed characters in URL and search

[eluser]victorche[/eluser]
[quote author="Buso" date="1280146169"]http://ellislab.com/forums/viewthread/160377/

If you need to whitelist more characters you can do that in config.php.

It is about security as you said, but you can change almost anything in CI.[/quote]

Thanks, Buso ... This helped a little. I have 2 different questions. The first one:
As I am a newbie in programming, the solution you are giving there seems elegant, but can you give me a hint (short example) what should i do next in MY_Router? I mean this part of your answer "Then you let the Router class handle that as a 404". Can you please give some more info about it?
The second question is more about the logic. If you want to search for "iphone" and by mistake you type "iphone>", do you think it is normal to lead to 404?
Because the user who asks in the other topic has another problem. Not like mine. He needs after submitting a disallowed character - 404 page. I don't think this is good for my case. I can't even think of a website, which has a search function and this search leads to 404 in any case
Maybe i will prefer just to search for everything, or ... if it is not possible, just to have an error message, informing for the not allowed characters (but not the default CI one).

Sounds too complicated, i know. But as i said, i don't think there is a site, which gives 404 or "disallowed characters" as a result for search