Because of Cydoor's highly controversial practices of running ads in software programs, Cydoor software is often considered spyware — and many Anti-Spyware and Antivirus applications will flag the software as such.
The Cydoor software downloads advertisements from the Cydoor servers, to be displayed in the Cydoor-supported software.
Cydoor consumes about 3.4MB of hard drive space, and cannot be uninstalled using the Windows uninstaller. No uninstaller is provided. Cydoor is often bundled with commercial P2P filesharing programs such as Kazaa, FlashGet or eXeem.
Formerly, a user could uninstall Cydoor and continue to use the program installed with it, but that is sometimes no longer the case. Now Cydoor is treated as a vital piece of software code by the parent program, and removal may cause the program to stop working. The website's FAQ explains, "Our components...are the main revenue generating components for our software partners," as the way of explaining their supposed necessity. Though, hackers have successfully removed Cydoor's software from Kazaa (resulting in Kazaa Lite and Kazaa Resurrection).
The program has been known to cause problems in Windows, but the company asserts that this is due to an old and buggy version of the software. They also claim not to harvest personal information unless "the user voluntarily supplied it".