Did you just run into a download or a file on your computer that has been digitally signed by AT&T Inc? If so, please read on.
You'll typically see AT&T Inc when double-clicking to run the file. The publisher name is displayed as the "Verified publisher" in the UAC dialog as the screengrab shows:

You can also view the AT&T Inc certificate with the following procedure:
Here is a screenshot of a file digitally signed by AT&T Inc:

As you can see in the screenshot above, the Windows OS reports that "This digital signature is OK". This implies that the file has been published by AT&T Inc and that no one has tampered with the file.
If you click the View Certificate button shown in the screenshot above, you can examine 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 examine the address for AT&T Inc, such as the street name, city and country.
VeriSign Class 3 Code Signing 2009-2 CA has issued the AT&T Inc certificates. You can also view the details of the issuer by clicking the View Certificate button shown in the screenshot above.
These are the AT&T Inc files I've collected, thanks to the FreeFixer users.
| Detection Ratio | File Name |
|---|---|
| 0/40 | att.dll |
| 0/43 | ToolbarSvr.exe |
The detection percentage is based on the fact that I've collected 83 scan reports for the AT&T Inc files. 0 of these scan reports came up with some sort of detection. If you like, you can view the full details of the scan reports by examining the files listed above.
The analysis is based on certificates with the following serial numbers: