Outlook Argus is an Outlook 2007 add-in that will scan the contents of out going mail messages before they are sent looking for patterns of information that are sensitive (the two supported are credit card numbers and social security numbers). The idea isn't to block these e-mails but to prompt the user for confirmation to send them in an attempt to raise awareness to what is being sent over e-mail. The confirmation dialog will give examples of the matched pattern and what it matched (the user can then confirm to send or cancel to return to the message without sending).
In a time where you read about privacy concerns everyday in the news I thought this would be a worthwhile (and very simple) project to raise awareness. Pattern matching on small numbers provide false positives especially in business where other ID numbers that could match the patterns are used (in those cases this may not make sense to use or the regular expression patterns maybe able to be changed to fit your needs). I've been using this filter for a month or two and have only violated the filter with a false positive once. In the next release I plan to have the credit card filter go a step farther and figure out what type of credit card it is before that pattern will be triggered to hopefully mitigate false positives in that instance.
This project was written in Visual Basic against the .Net Framework 3.5 using Visual Studio 2008. It only supports Office 2007 at the moment though the code could easily be moved into an Office 2003 component project (if there are requests for that I would go ahead and put that project together and add it into a release here).