If the controller is a 840Di series then it would be windows based and I think most siemens are I think.
The ethernet net is used for maintenance only
If you connect the ethernet on a network then it can be infected by viruses / worms ect.
My advice is not to
There is a password to get on and it is well known this password and it will let you access all parts of the controller.
Someone only has to make a little mistake and the controller will not work correctly.
Personally just keep using the RS232 or USB.
I believe there maybe some software but I'm told it is expensive
There are several companies use eithernet for there machine but have discontinued there use due to Hacking as most users have them on a network which is connected to the ethernet.
I have come across one case that a network kept alarming that they had a virus on a Fanuc so they had to be diconected from the network
I hope this gives you some insight in what precautions and action to take