Can you get StackOverflow to "sponser" this idea? Not just for crypto (which you've done) - but for all PHP related answers?
Because the problem is there are many "old" accepted answers, with high upvotes, that will always come up as number 1 or 2 in google searches.
Given PHP has changed so much, many of those answers are outdated, use incorrect and insecure methods, and some are now just wrong. This is not just security - but a whole host of answers.
The "meta" StackOverflow rules will tell you to downvote the old answer and post a new one - but that is not practical - and will take years to take effect. Plus, many people simply read the first large upvoted answer, copy + paste the code, and move on.
edit: I guess it would be nice to be able to "flag" an accepted answer (not a question) as outdated, get 5x people with gold badges for that tag to accept it - and then the answer is highlighed as wrong/out of date (or even deleted). Something like that.