Back in 2019, a massive security flaw was discovered in WinRAR that had actually existed for nearly 19 years. The issue wasn't with the RAR format itself, but with a library called UNACEV2.DLL that WinRAR used to extract files in the older .ace format.

Use the latest version of WinRAR or switch to modern, open-source alternatives like 7-Zip or the built-in extraction tools in Windows 11.

Even if a file is named old.rar , it might actually be an ACE file disguised with a different extension.

Be wary of archives that contain executable files ( .exe , .scr , .vbs ) inside them, especially if they claim to be just "photos."

If you are still using a legacy version of WinRAR or another extraction tool to open your old archives, you are essentially leaving the door unlocked.

Hackers figured out they could rename a malicious .ace file to .rar . When a user with an outdated version of WinRAR (anything below version 5.70) tried to open it, the software would unknowingly trigger a "path traversal" vulnerability. This allowed the archive to drop a malicious file into your Windows Startup folder without you ever knowing. Why "Old" Matters