It's possible that I'm not correctly stating my problem, because I've posted this question in a couple of other forums (fora?) with little success. However, I desperately need a solution to my problem, so here's my question:

How can I prevent a user from opening another workbook in an Excel session "from the outside"?

I'm fairly new to VB. I'm developing (in VB 2003) a simple but SECURE Excel environment which will allow a user to update a hidden Master_Records workbook. I need to keep the user's Excel session secure...for example, I've disabled all Excel Toolbars and Command Buttons, effectively preventing the user from doing anything except filling in some cell values and clicking on a few custom buttons in the worksheet. But how can I prevent the user from opening another workbook into the active session from his desktop and introducing some malicious code into the session via that route?

One respondent in another forum (the only one, in fact) suggested that I look into "instantiating workbook level events" so that I can detect when other workbooks are open. I'm not sure what that means, is there someone here who could give me some guidance into that solution?

Thanks in advance,
Mark