A ZIP file is either a file on a Zip disk or a compressed file or collection of files made into an archive using the ZIP format. The Zip disk is a product introduced in 1995 by Iomega that is similar to floppy-disk technology. The disks are available in 100MB, 250MB, and 750MB variations. The 3.5 inch (8.89 cm) disks are transportable and rewritable and, like a computer, can hold a wide variety of varied types of files, so in this case, zip file can be pretty much any file small enough to fit on a Zip disk.
After Phil Katz developed algorithms for file compression in the early 1980s, he designed the programs PKZIP and PKUNZIP, which were produced by his company PKWARE for the DOS operating system. The ZIP standard was developed by Katz in 1986 and the algorithms for both zipping and unzipping were placed in the public domain. Other companies then created ZIP utilities, including Nico Mak Computing — sometimes rendered as “Nico Mac” — which became WinZip and was acquired by Corel, and Netzip, made by Software Builders International. WinZip is a ZIP version for the Microsoft Windows operating system, and PKWare now also makes ZIP for Windows, while MacZip is made for Apple computer users and Zip and UnZip work on UNIX. A split in the ZIP standard occurred between 2001 and 2003, when PKWARE and WinZip went in different directions using different specs.
Some files that do not have a .ZIP extension are actually ZIP files. These include JAR files with a .jar extension and Open XML files in Microsoft Office 2007 with a .docx extension. Besides ZIP files, there are other file extensions that include or reference the word zip and archive, compress, or both. These include 7-zip, ALZip, bzip2, gzip, lzip, and rzip.
In May 2010, several types of malware attacks using ZIP files surfaced. In the first case, the malware is offered through an innocent-seeming instant message on Yahoo! Instant Messenger or Skype, but when the image file is clicked, the ZIP file offered for download contains a worm. In a similar timeframe, security vendors notified the public that Human Resources departments were being targeted with an email that appeared to have a job resume attached in a ZIP file, but the ZIP actually contains malware.