Did you just stumble upon a file that has a digital signature from Stefano Nigsch? If that's the case, please read on.
You'll typically notice Stefano Nigsch when clicking to run the file. The publisher name shows up as the "Verified publisher" in the UAC dialog as the screenshot shows:

You can view the additional details from the Stefano Nigsch digital signature with the following steps:
Here's a screenshot of a file digitally signed by Stefano Nigsch:

As you can see in the screenshot above, Windows states that "This digital signature is OK". This implies that the file has been published by Stefano Nigsch and that no one has tampered with the file.
If you click the View Certificate button shown in the screencap above, you can see all the details of the certificate, such as when it was issued, who issued the certificate, how long it is valid, etc. You can also view the address for Stefano Nigsch, such as the street name, city and country.
UTN-USERFirst-Object has issued the Stefano Nigsch certificates. You can also view the details of the issuer by clicking the View Certificate button shown in the screenshot above.
The following are the Stefano Nigsch files I have gathered, thanks to the FreeFixer users.
| Detection Ratio | File Name |
|---|---|
| 0/43 | SLAntiSpamLSP.dll |
The detection percentage is based on the fact that I have collected 43 scan reports for the Stefano Nigsch files. 0 of these scan results came up with some sort of detection. You can review the full details of the scan reports by examining the files listed above.
The analysis is done on certificates with the following serial numbers: