I'm just using it on a private network so I don't much care about security and haven't looked into it much. It's the most basic level of windows security (no domain controller or anything). I don't know how secure that is i.e whether passwords are clear text/sniffable on your work network.
One thing I suggest you do is just share your book/document directory - don't share the root/iRex filesystem - even if it is just you accessing it you wouldn't want to accidentally send iLiad system files to the windows trashcan!
Then security wise, presuming you are backing up those books/documents elsewhere at work, I guess it just depends on whether you care about someone determined seeing what's in your book/document directory.