Yeah, social engineering can get people to install software that's bad for their system. FWIW, on my Mac, there are several flags to warn you, but you can overcome them. First, if you download an application, you're warned it's an application before it completes download. Second, even if you're logged in as an administrator, you still have to enter the admin password to install (that's a serious flag.) Third, the first time a program executes, you have to give it permission to run, permission to access the keychain, and permission to access the internet.
But YES, if you ignore all this, you CAN install a trojan on a Mac. I suspect the same is true for Linux.
Not if you use the console, for sure. Even using the GUI, I haven’t seen any warnings about opening files, but I don’t usually use the GUI fro installing downloaded apps.
But then, I never try to open something without knowing what it is first.
99% of all the software I install, comes from the Ubuntu repository, the other 1% is downloaded from trusted sources.
The Mac precautions you mention must be what MS copied into Vista, eh? (My newest Mac is 10 years old-LOL)