router concerns

hi

i have just found out i have a modem+router device that has no hardware firewall. or so i think i am not sure... i wasnt the one who made the setup so..

anyway, my current router is a repotec RP-IP1800

N.B i read on some article that i may add SPI firewall to the mentioned router if it is conexant based with CX82310 chip
see this link http://www.routertech.org/viewtopic.php?p=7583 of course i dont know what that mean

my current router info is
Firmware Version: CX82xxx_4.1.0.9_S
Customer Software Version: 4.1.0.9
i have NAT enabled with NATP as mode

1 >>>>>>>> i would like to know how secure it to use that router, is it safe to use it for internet access when i will be doing online banking and other sensitive uses

2 >>>>>>> if so how to configure it for maximum security.. when i log in to there are a lot of things/options/..etc.. i dont know how to tweak it



3 >>>>>>>> how can a router+adsl modem be a source of malware infection, can it be infected it self , how it is used by malwares to harm users

i have just realized that routers+modem are security related, i always thought they are just dumb devices that allow net access and thats it


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here is an explanation of my network setup'

first of all, i will be sharing the internet connection with other computers that i have no control over them nor trust their security.. so i want to BLOCK all networking activities with these pcs to avoid any malware infections.. BUT allow internet connection sharing.

4 >>>>> is this safe? i use my pc for sensitive information and i want to be safe from network based malware, will only allowing internet sharing accomplish that?


what router+adsl modem do u recommend i purchase?
i only use wired internet acces
and i would like you to consider the price factor as my budget for a the new router is very tight and all i am looking for in it is security security

my main feature in the router would be security as this is the main reason i getting a new one

and would you kindly tell me how to configure that router to meet my needs;

5>>>>>>>>>>>>>>>>- only internet connection sharing is allowed
maximum security configured


I NUMBERED THE Q's since the post is long and not really organized

i would greatly appreciate your help since i am a complete newbie in this field

thanks a lot,