Note: This is for IIS 6.0.
- Open IIS Manager.
- Browse to the IIS Site or subfolder where the .DAT files are
- Right-click on that site or subfolder and select Properties
- Select the HTTP Headers tab
- Click on the MIME Types button
- In the extension box, type ".dat”
- In the MIME Type box, type "application/octet-stream"
- Click OK