Btw my friend needs a sandbox for his mac, because he haves this habit of downloading files unsafely, does anyone have any ideas of a sandbox he can use.
Whoops... Let my clarify. I should say that if you don't enter your username/passcode then you can't install software. Of course, the software can still download. However, that's not to say that Mac doesn't get malware. For example, if you get a pdf file with viruses in it, or a trojan acts like a legitimate file and you try to install it. Browser Ransomware is also a problem. Still, the biggest problem is phishing threats as those are not depended on OS or even download/installation. So watch out for phishing threats by using Bitdefender TrafficLight or WOT (or Adguard For Mac if you are willing to pay money).In such case of Mac OS, watch through the program he/she downloads as usually those .dmg are executable files and may access uncontrollable if the account is Admin.
I think you need to consider running Mac Antivirus which isn't bad idea, even though it includes Windows signatures detection therefore any assurance that will not run due to OS environment.