It's a fundamental problem with QR codes, You don't know what it contains until you scan it. I advise caution when scanning any code.
There have been cases where publicly placed codes have been changed, Redirecting users to malicious web sites.
Correct! But I suppose they have something like a plastic foil sticked on the code so no one can change it. You know what I mean? I dont know how to explain as english is not my mother tongue.