This information applies to Windows Internet Explorer 8.
It can be frustrating when a program changes your default search provider, especially if the provider is changed without your permission. But it's also preventable. Whenever a program such as an add-on or toolbar tries to request a change to your default search provider, Internet Explorer displays a dialog box that lets you make the decision whether to keep or change your current default provider.
If you want Internet Explorer to always block changes to your default search provider, you can select the Prevent programs from suggesting changes to my default search provider check box in the dialog box that appears when a program attempts a change.
You can also do the same thing by following these steps:
Open Internet Explorer by clicking the Start button , and then clicking Internet Explorer.
Click the Tools button, and then click Manage Add-ons.
In Manage Add-ons, under Add-on types, click Search Providers.
Toward the bottom of the screen, select the Prevent programs from suggesting changes to my default search provider check box, and then click Close.