It is possible to hack any website including Google, Yahoo, Bing, Ask, whatever you want. But as a rule of thumb, the more popular the site, the harder it will usually be to hack as they will have more teams of developers and more security. If I had hundreds of people working for me for months, even years, we could probably work and hack Google for like 10 minutes. Seriously, if you want to hack a search engine then you would at least need to start with a small, less known one. If you're really experienced with coding you could probably hack a small one but it wouldn't even be worth the effort at that point and bigger ones are out of the question.