These are either badly written paid-for negative reviews or reviews written by people with really poor, and I mean really really poor basic computer skills.
I have never had an issue with DDG hijacking anything I use - it is installed on all my devices - and I have selectively allowed third party cookies with no issue. No spam email, no hacking, and as the first entry is an ad ( as they say) and it is marked as an ad, I have no real problem scrolling past it.
If your computer was hacked, that sucks, but did you install from Duckduckgo or a third party. Is your firewall up to date or did you turn it off to install something? Are you just really crap at keeping you computer secure and forget that it is your responsibility, not the software's, to be up to date?
The quality of the results is better than Google, who, as other reviewers have mentioned, are concentrating on ad revenue rather than quality, and far better than Bing ever was (if you are looking to be paid for writing negative reviews, try Bing, just sayin)