Security on wirelss lan, what can a hacker all do, Problems, please help

[iser]

Hi
We have a wireless lan installed with 3 computers. We have an outside antenna where the wireless lan can reach over 1000 meters and there are 3 computers connected.
There are no securities installed.
What I wanted to know ist the following:
Could a hacker break into the computers and manipulate files or install all kinds of files .
Could he remotley controll a computer and auction something on the internet?
Could he install all kinds of files to make someone look a bad person.
What else can he do?

Please help.
Thanks ahead

[M/Q]

If you do not have any security measures in place, someone could do anything that you can do by plugging into the wired portion of the network. If you have domain-centric environment, there will be some access control, but that is about it. How you have the Internet access configured will also determine if someone without network authentication can gain access to the Internet.

There are other considerations as well. Again with no wireless security, any vulnerability be displayed by the network operating systems or individual clients will be an avenue for penetration and compromise of the network.

I am not sure why you are not adding at least some sort of control on the extended link. It appears to be a bridge link and that can be locked down very easily with address control.