I think your browser settings have been comprised sending your browser requests through a third-party proxy server which is sending your search requests to sponsored sites where the perpetrator has a revenue sharing arrangement. It's easy to check. In Firefox go to Tools > Options > Advanced > Network > Connection Settings. If a proxy server is enabled that is unfamiliar to you, change back to "no proxy". This should take care of the issue assuming a piece of resident malware on your computer does not reenable the spoofed proxy server.

IE settings are likely similar.

Good luck.

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Pat Riley