HTA stands for HTML Application. It is a Windows file type that can contain HTML plus script, and when opened it runs through the Windows HTML engine with the user’s local privileges. Unlike a normal web page, an HTA is not confined by browser sandboxing, so it can access files, launch programs, and perform system actions.
HTAs matter in cyber security because attackers can use them as a proxy execution method: a seemingly harmless .hta file can start malicious script or drop other tools, often through mshta.exe. Defenders watch for unexpected HTA files, suspicious use of mshta.exe, and chains that combine downloads, scripts, and unusual child processes. If HTA use is not required in an environment, blocking or restricting it is a strong hardening control.