While ZIP files are the standard for sending batches of files easily via email, they have notable vulnerabilities:

: These are specialized archives that, when unzipped, contain an identical copy of themselves. This creates an infinite loop or "round" during the extraction process.

: The format identifies frequently occurring patterns (bytes) and replaces them with shorter bit sequences.

In the context of complex ZIP structures, "rounds" typically refers to the process of —zipping a ZIP file repeatedly to achieve extreme file size reductions.

To understand why "rounds" of zipping work, it helps to know the basics of how ZIP files operate :