There are a lot of ways to protect your computer. If you are very concerned about virus and bla bla you should have anti virus software installed, update it all the time. remove spy ware and update your windows.
You are almost safe.

the second both those computers are connected to the router and are on the Same ip range its a network.

and honestly unless your ultra paranoid sharing a holding isn't any issue.

your more likely to get a virus from web surfing then to get one from sharing a folder on a network behind a well set up router

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Hi.... how do you do ! nice to meet you.
this pic is very interested.

Hi Taichan !
It has nothing to do with IP address. Your computer is connected to internet,
I can access to your share folder. you know ?
I can know all your computer resource. Today, there's a many hacking tools.
you know ? And MicroSoft Windows have a many problems for the security.

a router is a NAT firewall, someone has to be trying to hack your network to really do it. and honestlly if someone is that bored they're trying to hack me, let them do it as i don't bloody care enough of some hacker wannabe is trying to get into my computer.

a real hacker will not go after a presonal computer

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Hi my sister .
Router is a very simple Network equipment and it's only working at L3.
Do you know L3 ? L3 is a Network layer in OSI 7 Layer.
Do you know OSI 7 Layer ?
The Router don't prevent everythings. you know ?
Router only can prevent IP address and TCP/UDP port.
Even though you have a NAT IP address, some hacker or some virus can access into your computer.

I took the Cisco CCNA classes though i never took my test so yes i know what a L3 is. i also know i have my router setup to ignore pings so it doesn't respond to them as well as shunt DOS attacks to ground to keep it form overloading and i also know NAT is a firewall if setup to be, which mine is.

unless you have your router setup to foreword a port ot your computer, if you don't then you have to your computer has to ask for the packet to get it diliveried to your system

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OK..IC....
so, do you know about well-known port ?
for example, number 80 port is web access port you know....
you can't prevent this number on your router.
can u understand it ?
but some virus or some hacker can access to your computer through this port.
you know it ?

True but if you set up acl's to restrict most protocalls then you will be fairly safe. Desk top firewall like Zone Alarm or one of the others is ok. Now for a major network then you set up other things like IDS, honey pots, DMZ ect. Taichan is correct only an inexperienced Hacker will go after a personnel PC and if you put a few blocks up it will discourage them. I look at it like my car I lock the door and set the alarm but someone that really wants it will still get in. the locks keep honest people out. Any computer can be hacked given enough time and ambition.

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Just my humble opinion!