I can only assume that they suspect you of being some kind of a search bot, making millions of searches a minute, since only this kind of a search would cause them problems. I doubt they would care about the content of the actual search, and wouldn’t try to stop you from making certain types of searches they might disagree with politically. This could be possible if maybe some bug on your computer is doing these random searches without your knowledge.
I think that is correct.
I have only gotten those prompts when I am searching and not finding what I want. I keep changing the terms or I start a new search with keywords garnered from a previous search and quick review of the front page results.
I do tend to use Ixquick and Start Page for most searches. I really don’t see much difference in the results. I read that Ixquick is following EU rules on privacy, so I think we can trust their statement that they don’t record IPs.
I gather that if you do not have Gmail open when searching Google, then you don’t get the keywords thrown back at you via ads. Is this true? I don’t use Gmail. My ISP provides a web mail and I use Eudora at home and the web mail when on other computers or traveling.
However: the history on any computer is open to authorities. They do know which sites you regularly read.