Doesn't have to be not logged-in. Years ago I use Chrome (with myself logged into Google) to search for very specific queries, so I have to use multiple operators (double quotes, "site", "filetype") in one search to narrow the result. I was hit with CAPTCHA as soon as I browse to page 2 of the result. This happens many times, so I have to do this kind of search at different times to make sure it doesn't see me a heavy traffic at any point.