Suppose there were a cheap way to make nuclear weapons out of common household materials. Knowing this information is not directly harmful to the median individual like yourself. On average, it may even be beneficial to the average person, to know that secret yourself; either because you could directly conquer places, or because you could sell the info to somebody who could. But society as a whole would rather that nobody knew it than that everybody knew it.
For a more realistic example, consider the DNA sequence for smallpox: I'd definitely rather that nobody knew it, than that people could with some effort find out, even though I don't expect being exposed to that quoted DNA information to harm my own thought processes.
'Infohazard', I think, should be used only to refer to the slightly stranger case of information such that the individual themselves would rather not hear it and would say, "Don't tell me that".
A spoiler for a book you're in the middle of reading is the classic example of information which is anomalously harmful to you personally. You might pay a penny not to hear it, if the ordinary course of events would expose you to it. People enclose info about the book's ending inside spoilers, if on Reddit or Discord, not because they mean to keep that secret to benefit themselves and harm you - as is the more usual case of secrecy, in human interactions - but because they're trying to protect you from info that would harm you to know.
The term 'infohazard' has taken on some strange and mystical connotations by being used to refer to 'individually hazardous info'. I am worried about using the same word to also refer to information being alleged to be dangerous in the much more mundane sense of 'collectively destructive info' - info that helps the average individual hearer, but has net negative externalities if lots of people know it.
This was originally posted by me to Facebook at greater length (linkpost goes to original essay). Best suggestions there (imo) were 'malinfo' and 'sociohazard', and if I had to pick one of those I'd pick 'sociohazard'.
EDIT: I like shminux's 'outfohazard' even better.
EDIT 2: My mind seems to automatically edit this to 'exfohazard' so I guess that's what the word should be.