PKZIP does have an encryption feature, based on a proprietary algorithm, but they don't seem to talk about it much and readily admit that it's vulnerable to brute-force attack.
Security is based on a password of up to 255 characters which is used to encrypt the zipped files. But there are numerous tools available to crack the passwords, and few users seem to have any real faith in PKZIP security.
The company is believed to be working on a stronger version of the algorithm, but no word yet on details or a release date.
The product also has a digital signature feature for authentication.
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This was first published in March 2002