Ultimate Packer for Executables

 UPX Github
https://www.esecurityplanet.com/threats/upx-compression-detection-evasion/

Ultimate Packer for Executables (UPX) is an open-source Executable Packers that can reduce the file size of an executable drastically (better than Zip files), and it is compatible with a large range of executable formats, like Windows DLLs, macOS apps, or Linux ELF.

Also read: How Hackers Evade Detection

The packed file is usually smaller on disk but bigger in memory. If you inspect a suspicious file, you might see typical sections like the following:

• UPX0: An empty section that contains no actual raw data but with a huge virtual memory size
• UPX1: The stub and the compressed executable

There are other sections, but we’ll keep it simple here.