One programmer left his initials inside every ZIP file you open

I’ve probably opened thousands of ZIP files without thinking much about the format itself. Double-click, extract, move on. Then I learned that if you peel away the friendly folder icon and look at an ordinary ZIP archive in a hex editor, there’s a tiny calling card buried in the machinery: 50 4B. In ASCII, those bytes read PK, the same initials as Phil Katz, the programmer behind PKZIP and one of the people who created the ZIP format.