Active Scanning doesn't allow you to exclude OUs. You can only do the reverse: specify that only specific OUs should be scanned. Note that:
- All scanning methods work independently. Machines submitted for IP Address Range Scanning will be scanned regardless of whether or not they're submitted for Active Scanning as well. You will need to check each scanning method's configuration.
- Changing your configuration only affects future scan attempts. To delete unwanted machines that have already been scanned, click the Assets link at the top of the web console, tick the checkboxes in front of the assets and hit the Delete button on the left.
- IP exclusions only affect IP Address Range Scanning. To exclude Windows computers from all scanning methods, you should submit their NetBIOS names in the Windows Computer Scan Exclusions section of Configuration/Scanning Setup/Scanning Methods. You can use % as a wildcard. E.g. %lan% excludes any computer whose name includes the word "lan".