Internet Explorer 4 was released to the public on September 22, 1997, and deepened the level of integration between the web browser and the underlying operating system.

The integration with Windows, however, was subject to numerous packaging criticisms (see United States v. Microsoft Corp.).

Internet Mail and News was replaced with Outlook Express, and Microsoft Chat and an improved NetMeeting were also included.

Uninstalling IE4 became the subject of concern to some users and was a point of contention in later lawsuits (see Removal of Internet Explorer and United States v. Microsoft Corp..) On January 6, 1998, at the Macworld Expo in San Francisco, Microsoft announced the release of the final version of Internet Explorer version 4.0 for Macintosh.

Version 4 includes support for offline browsing, Dynamic HTML, a new faster Java virtual machine and Security Zones that allow users or administrators to limit access to certain types of web content depending on which zone (for example Intranet or Internet) the content is coming from.

At the following year's San Francisco Macworld Expo on January 9, 1999, Microsoft announced the release of Internet Explorer 4.5 Macintosh Edition.

[2] On January 27, 1998, it was reported that IE 4.0 for Solaris was due in March; Tod Nielsen, general manager of Microsoft's developer relations group, joked that "he wanted to launch Internet Explorer 4.0 for Unix at the Ripley's Believe It or Not!

[4] Other new features including Dynamic HTML, inline PNG, Favicons, a parental rating system, and the ability to 'subscribe' to a website in favorites, where it would notify the user of an update.

This changes the way you look at Windows, with files and folders now acting like hyperlinks on a Web page; you move your cursor over them to select them, then single click to launch.

For instance, the WebBrowser control can be added to a C++ program and MSHTML can then be used to access the page currently displayed in the web browser and retrieve element values.

A Browser Helper Object (BHO) is a DLL module designed as a plugin for Internet Explorer 4.0, and provides added functionality.

[19] Internet Explorer 4 supported 40-bit and later 128-bit encryption through an add-on,[20] using Server Gated Cryptography (SGC).