We can’t know. If we would know, those weren’t undetected backdoors at all. It’s not possible to know something you don’t know. So the question in itself is a paradox. :D The question is not if there are backdoors, but if the most critical software is infected? At least what I ask myself.
Do you backups man, do not install too many stuff, do not trust everyone, use multiple mail accounts and passwords and 2 factor authentication. We can only try to minimize the effects of when something horrible happens. Maybe support the projects you like, so that more people can help and have more eyes on it. Governments and corporations with money could do that as well, if they care.