Thanks to Mertsch in our forums fyi. Improvements in WinZip 9.0 concentrate on its core functionality: compression, capacity, and a new, advanced data-encryption capability. Using WinZip 9.0, you can compress more data, compress it better, and protect your sensitive documents with far greater security.

Major Changes in Version 9.0: Advanced encryption
WinZip 9.0 supports 128- and 256-bit key AES encryption, which provide much greater cryptographic security than the traditional Zip 2.0 encryption method used in earlier versions of WinZip. Greater capacity
In addition to supporting the original Zip file format, WinZip 9.0 also supports the 64-bit extensions to the Zip file format. The extended format lets you store all the data you need in Zip files of virtually unlimited size. Improved compression
The compression method previously listed as "Maximum" is now listed as "Maximum (portable)." This is to distinguish it from "Maximum (enhanced deflate)." WinZip 9.0 supports the "enhanced deflate" compression method. This compression method provides greater compression and reduces the size of your Zip files, saving you data transmission time and valuable disk space. More changes here
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