This could also be Google probing for vulnerable software on your website. They're doing it for various Typo3 versions (I know, because we got some false posit

This could also be Google probing for vulnerable software on your website. They're doing it for various Typo3 versions (I know, because we got some false positives in the past - Google Webmaster tools warned us about it, we saw the requests in logs, our fault for replying with Status 200 for some invalid URLs where we just showed our main page), they might be doing it for other software where the only way to check for vulnerabilities is to try an actual (harmless) SQL inject.