Say you're about to drive over a cliff edge, the obvious thing I can do is 'warn you about it', but I can also 'warn you not to do it' because it's dangerous, etc.
If I instead 'warned you to drive over the cliff':
- something else needs to follow - 'or else I will do something worse to you' for example
- it means that you should (IMO - my *fictional* O!) do it
If you want that more active phrasing, the unnegated infinitive 'to drive', or 'to use' rather than 'to avoid' the site, you need to say something like 'caution against' instead of 'warn'.It could have been:
> Police caution students against using science website
A warning is either about a bad thing:
> Science website considered harmful, police warn
Or a strong suggestion for corrective action:
> Don't use science website, police warn
> Police warn students not to use science website
> [The submission]
"warning someone to avoid something" suggests that there is a risk associated with the thing itself - they should avoid the thing
"warning someone about avoiding something" suggests that there is a risk associated with avoiding the thing - they should not avoid the thing
(e.g., "HMRC warns people about avoiding paying income tax")
Science website sounds off to me for speaking about sci-hub. The title felt a bit like police advised students to distrust science.