Mainstream antivirus (Norton, McAfee, Windows Defender) scans for binary executables. AutoCAD viruses are and run inside the trusted AutoCAD environment. Your standard AV sees acad.vlx as a harmless text file. It isn't. It is a logic bomb waiting to detonate inside your CAD session. This is why you specifically need to download AutoCAD anti-virus protection designed to parse LISP syntax.
Standard antivirus programs often struggle to see inside specialized CAD files like .lsp or .fas . This gap led to the development of specialized protection methods:
To prevent AutoCAD from freezing or DWG files from becoming "read-only," Autodesk recommends excluding specific folders and file types from real-time scanning. Autodesk Community, Autodesk Forums, Autodesk Forum
is often more reliable than the "Install Now" method, which may be blocked by firewalls. Untrusted Sources