The Upwork desktop app is completely safe. However, because it uses various API technologies to capture and record screenshots, some virus scans mistake this capturing and transmitting of information as potential spyware or malware.
We assure you that the information collected by the desktop app is kept private between you and those you work with on Upwork. The app poses no security threat to your computer system. Avoid getting these warnings or black screenshots in the future by adding the desktop app to your security scan's whitelist. In Webroot Antivirus you'll need to allow upwork.exe in "Identity Protection."