11!!1!yyyyyddccmcmmm.7z

: At the bottom of this "nesting doll" structure are simple files filled with repetitive data (usually null bytes or zeroes). Because this data is extremely uniform, compression algorithms like LZMA can shrink it down to nearly nothing.

: Files like this are typically created as a proof of concept or as a "malware" tool intended to crash antivirus scanners or systems by exhausting disk space and memory during the decompression process. History and Context 11!!1!yYYYYDdcCmcmMm.7z

: Most modern antivirus programs and operating systems now recognize these recursive patterns and will block the file or stop extraction to prevent a system crash. Practical Use : At the bottom of this "nesting doll"