msiexec is the Windows Installer command-line utility. It is normally used to install, repair, or remove software packages in MSI format, and it can also be called with options that download or launch installer content from a command line.
In cyber attacks, msiexec matters because it is a trusted Microsoft component that can be abused as a “living off the land” tool. Instead of dropping an obvious malware executable, an attacker may trick a user or script into running msiexec with a remote URL, a malicious MSI file, or an encoded command. That can help the activity blend in with normal system administration. Defenders watch for unusual msiexec launches from browsers, email clients, scripts, or ClickFix-style prompts, especially when the command reaches out to the internet or spawns unexpected child processes.