The safest way to get Mpasmwin.exe is not to download it alone, but to download the last version of the legacy MPLAB IDE that included it.
If you have found yourself searching for you are likely looking to resurrect a legacy project, maintain older code, or set up a classic development environment on a modern machine. While the industry has moved toward the XC8 compiler and MPLAB X IDE, the standalone MPASM assembler remains a vital tool for many. Mpasmwin.exe Download
Many shady websites offer "Mpasmwin.exe download" as a 1MB standalone file. These are almost always malware, DLL hijackers, or keyloggers. Never download Mpasmwin.exe from third-party DLL sites. The safest way to get Mpasmwin