Should test data be used in production?

We are deploying an update to our main application in production. The update has been tested in QA and it looks good to go. Our client wants to do a test in production. For that case, we will run the application using "test data" in production and once the test has been finished, we will delete the "test data".

A couple of server admins are against this because "test data doesn't belong to production". I think it's OK since the QA server and the production server have different hardware and the databases house different applications (QA has more databases, production is dedicated). Besides that, are there other facts that I can use to back my opinion?

EDIT: adding context

The application is a tool that automates the reception and validation of data. We receive the files via email and this tool automatically validates them and imports them to the database. We have a BI system that creates reports using this information (excel files are received by email, then validate, then reports/views come out, all this automated).

The "test data" would be old files (good and bad files from previous efforts) that represent true data (actually it is true data but with problems or just too old).

Solution

Your admins are right. Having test data in production will expose you to the risks (security holes):

Test data in production can be used to do damage to your company (intentional or nonintentional).

For example if you have non excisting identities on production you can do payment to them. If they are linked to real bank accounts you lose money without the ability to detect it.

Test data can change your management reports. When having fake action, some can infuence reports and have impact on decisions made. This will very hard to track and even harder to correct.

Test data can interact with production data. If someone makes a mistake and make a wrong relation production data can be changed based on test data.

There is no good way of detecting you have test data, if you would mark it. All data can be marked as test data. If you handle the test data different in your businesslayer, it whould not be a real test of your production environent.