Generally, no, this string is not a virus or malware. It is a syntax error. However, it can be a symptom of a security misconfiguration:
Which application showed this URI? (Browser, proxy tool, script, etc.) proxy-url-file-3A-2F-2F-2F
Sometimes, software encodes a URL once (turning / into %2F). If that encoded string is then passed to another system that encodes it again, the % signs get encoded into %25. Generally, no , this string is not a virus or malware
Web server logs, firewall logs, or debugging output sometimes truncate long URLs. For example, a request to http://proxy-url-file:///config might be logged as proxy-url-file-3A-2F-2F-2F after escaping and trimming. Which application showed this URI
Some malware families use custom URI schemes to register protocol handlers, allowing them to launch automatically from a browser. For instance, if a user clicks proxy-url-file:///C:/malware.exe, the handler might execute it. The encoding %3A%2F%2F%2F would appear in logs, registry entries, or shortcut files (.url files).
If you need the actual URL that was intended:
Manual restoration:
proxy-url-file-3A-2F-2F-2F → proxy-url-file%3A%2F%2F%2F → Decode → proxy-url-file:///