Without seeing the asset page it is difficult to comment it. Possibly a computer was scanned from Active Directory. You need to ensure that DNS does not resolve to this hostname from the IP of the asset and that AD computer accounts get disabled as soon as the computer is not in use any more.
If you could not resolve the issue, could you send a mail to support@lansweeper.com with the following:
- Link to this forum topic
- screenshot of an affected asset page
- screenshots of your setup under Configuration\Scanning methods