Usually due to unsafe browsing or if you do not have an active antivirus running in the background, some viruses can hijack your browsers search engine. My recommendations would be to scan your computer fully with an anti-virus of your choice. I know for a fact that malware bytes and hitman pro usually can deal with these issues fairly well, but not certain, after cleaning it once, I recommend restarting your PC and doing it again. Afterwards, I recommend running an anti-virus of your choice, keeping your operating system up to date, as that increases security and be aware of the links that you browse, some links can be insecure and if you do not recognize the link properly, it is best to not browse it. Good luck!