Modem security

Auto dial-back is definitely not a bad way of securing, though depending on circumstances it might or might not be enough. A few other measures to consider:
* Authentication of the session by more than the remote system knowing the phone number, e.g. some userid/password or even better challenge/response.
* Encryption of either the whole session or the files transferred.
* Making sure the program on your modem's side can SOLELY do the connection for data exchange, nothing more (e.g. no complete IP session).

At your service,

- The Netherlands

AS you said, someone dialup into your network and probaly runs a script or a manually process in order to receive a file.
You should have the user modem logged in with the minimun rights possible when the cominication is taking place.
As you thinka user can send you a virus file or trojan horse.
But if is a DOS application which needs to dialup into someother place to retreive updates or some info, I think that you should ask your data-provider about the risks of that comunications.
Also what you need to check is to dial into that modem and see how the modem anwserd you and what options did it offers.
Example. if you have the windows authentication and a windows password ?s requiered, put a valid password and see in you can open a telnet session or an fpt session to another system. This can show you some vulnerabilities.

Hope it helps.

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