The main new features of WinZip 9.0 are:

• 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.
WinZip 9.0's advanced encryption (FIPS-197 certified) uses the Rijndael cryptographic algorithm which, in 2001, was specified by the National Institute of Standards and Technology (NIST) in Federal Information Processing Standards (FIPS) Publication 197 as the Advanced Encryption Standard (AES).
After a three-year competition, the AES was announced by NIST as an approved encryption technique for use by the U.S. government, private businesses, and individuals. When properly implemented as a key component of an overall security protocol, the AES permits a very high degree of cryptographic security, yet is fast and efficient in operation.
WinZip's AES encryption is just as easy to use as traditional Zip 2.0 encryption: all you have to do is select the encryption strength and specify your password.
In addition to the new AES encryption technology, WinZip 9.0 provides a number of usability enhancements that make it easier for you to use encryption. The most noticeable of these enhancements is the ability to easily encrypt the files that are already in a Zip file; previously, files could be encrypted only while they were being added to the Zip file.
Note: Recipients to whom you send AES-encrypted Zip files must have a compatible Zip file utility in order to decrypt the files. We have published the full specification for creating WinZip-compatible AES-encrypted Zip files, and we expect that other Zip file utility vendors will provide support for the format.

• 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.
The original Zip file format limited the number of member files in a Zip file to 65,535, and the maximum size of both the Zip file itself and any member file to 4 gigabytes. For all practical purposes, the 64-bit extended format eliminates all these restrictions. Using the extended format, the member file size, Zip file size, and number of member files you can add to a Zip file are limited only by your system's resources.
WinZip remains fully compatible with the original file format and uses the original format whenever possible. WinZip uses the 64-bit extended format only when the limits of the original format are exceeded.
Note: Zip files that are created using the 64-bit Zip file extensions require a Zip utility, such as WinZip 9.0, that supports this format in order to open these Zip files.

• Improved compression

WinZip 9.0 now both zips and unzips files with the "enhanced deflate" compression method. This compression method provides greater compression for many types of files and reduces the size of your Zip files, saving you data transmission time and valuable disk space.
The compression methods are now "None", "Super Fast", "Fast", "Normal" (the default), "Maximum (portable)", and "Maximum (enhanced deflate)" selectable from the WinZip "Add" dialog box.
Note: WinZip versions prior to 8.1 will not be able to extract files compressed with the "Maximum (enhanced deflate)" method. It may also not be compatible with some other Zip file utilities.
Other Changes in WinZip 9.0

• WinZip 9.0 makes it easier than ever for you to find the WinZip information you need by presenting help information using the newer Microsoft "HTML Help" facility. HTML help has a more attractive appearance and includes many usability improvements.
• WinZip 9.0 lets you quickly find out what is in your Zip files. In My Computer and Windows Explorer, the tooltip that is displayed when you position the mouse pointer over a Zip file now contains information about the contents of your archives by listing up to 25 of the files and folders in the archive.
• WinZip 9.0 includes "places bars" giving you easier access to your most important file locations in many WinZip Classic dialogs. Key dialogs such as New Archive, Open Archive, Add, and Extract contain "places bars" when running under Windows versions that support them. The Places Bar provides quick access to your top-level locations, usually My Computer, My Network (or Network Places), My Documents, Recent Documents (or History), and the Desktop.
• When installed under Windows XP, WinZip 9.0 installs and registers for all users. This change makes it easier to install WinZip in business or home environments where more than one person uses a computer.
• The main WinZip window now contains a watermark when used under Windows XP with an XP-style theme.
• WinZip 9.0 contains a number of changes to improve performance and efficiency:
• The "Use for removable media only" option for the working folder (in the Folders tab of the Configuration dialog) is now set by default. This results in faster Zip file creation in most cases.
• By default, WinZip no longer automatically displays comments when opening Zip files that contain comments.
• In Windows XP network environments, the performance of WinZip's Windows Explorer extensions has been improved.
• WinZip 9.0's Classic interface has been improved:
• The Extract dialog has been redesigned to display more folders in the folder tree view and to provide more space for typing folder names.
• Placing the mouse pointer over a truncated file name (one that won't fit in the available space) displays a tooltip showing the complete file name.

• Shortcut menus for files in the WinZip Classic interface main window now include commands associated with the file's generic type, if one is defined. For example, the menu for a bitmap (.BMP) file will now include any commands associated with the generic "image" file type as well as those that are explicitly associated with bitmap files.
• WinZip now supports the What's This? menu for many dialog controls. To display brief help information for a dialog control, simply right-click the control and click What's This? from the shortcut menu.
• The animated dialogs that appear when adding or extracting files now include a progress meter.
• WinZip now supports the New, Open, Favorites, Close, Print, and Send (mail) keys on keyboards with these "application" keys.