Websites using Adobe Reader, Adobe Acrobat, Apple Quicktime Player, Macromedia Flash and Sun Java Virtual Machine will no longer run automatically in Internet Explorer, following Microsoft's latest patch update last week.
Microsoft warned, "After you install this update, you cannot interact with ActiveX controls from certain web pages until these controls are enabled."
The change in functionality follows the settlement of a case brought by Eolas Technologies and the University of California alleging that Microsoft had infringed their patents.
The updates affect Windows XP Service Pack 2, Windows Server 2003 Service Pack 1, Windows XP Professional x64 Edition, Windows Server 2003 x64 Edition, and Windows Server 2003 with Service Pack 1 for Itanium-based systems.
Microsoft has introduced a "compatibility patch" to give developers more time to adapt their sites to the changes.
"As soon as it is deployed, the compatibility patch will temporarily return Internet Explorer to the previous functionality for handling ActiveX controls," Microsoft said.
The firm said the compatibility patch would function until an Internet Explorer update is released as part of the June update cycle, at which time the changes to the way Explorer handles ActiveX controls would be permanent.
This is not the first time users have been asked to install a patch as a remedy in a patent dispute case. Before its £350m settlement with NTP, Research In Motion issued a patent workaround as an update to the Blackberry Enterprise Server software.
David Barron, a lawyer at Wragge and Co, urged users to check the wording of their software contracts, as it was likely that patching would be mandatory. "I suspect the software licence may say that you agree to take appropriate upgrades and patches," he said.