Version 1.2.4 has many changes over 1.2.3, including these improvements:

• Fixed bugs in adler32_combine(), compressBound(), and deflateBound()
• Wholesale replacement of gz* functions with faster versions
• As part of that, added gzbuffer(), gzoffset(), gzclose_r(), and gzclose_w() functions
• Faster Z_HUFFMAN_ONLY and Z_RLE compression for images and other specialized compression
• Added flush options Z_BLOCK to deflate() and Z_TREES to inflate() for finer control
• Added inflateReset2() and inflateMark() functions, the latter to aid in random access applications
• Added LFS (Large File Summit) support for 64-bit file offsets and many other portability improvements
• Updated examples in examples/ and updated third-party contributions in contrib/

The previous version 1.2.3 (July 2005) eliminated potential security vulnerabilities in zlib 1.2.1 and 1.2.2, so all users of those versions should upgrade immediately.

For more information and to download the source kit visit zlib.net