Check the settings of the specific ULP script you are running.
Some older or custom-made ULPs use a static filename like ULP.txt to store data before passing it to another process. Is ULP.txt a Virus? ULP.txt
If you do not have any engineering software installed and find ULP.txt in a sensitive system folder (like C:\Windows\System32 ), it could be a log file for a malicious process trying to hide in plain sight. Check the settings of the specific ULP script