Will OS X ever install anything suspicious without my express permission? I clicked a link (turned out to be Breitbart) that said "your Flash is not updated", despite the fact that I just installed it yesterday. The two choices were "Update" and "Ok". Strangely, there was no ability to simply dismiss the popup without clicking one of those buttons. I should have force quit Safari, but instead I clicked "Ok". Then it tried to download something! I immediately dragged it to the trash, but when I tried to empty the trash it said that file was in use! I don't recall clicking on it or giving it any instructions to open so I immediately pulled the plug on the computer. I was able to delete it once I restarted.

Three questions:

1) Why did the computer download software from a random site without being given permission?

2) Why did it say the file was in use when I very clearly did not open it up?

3) Can the Mac actually install this kind of garbage without my permission?
It will download anything if you told it to do so.

It will obey your commands, down to self destruct (kill it self) if you ask it to do it.

There are some preventative measures in place (but at your control) to make it safer (from you).

For example the Downloads:



In order to change this setting you would have to enter a Password. In your case it is probably set (by you) to Anywhere, and that is fine if you know what are the risks.

Hopefully you learned a lesson, and in the future close the web site asking you to Update or OK (they mean the same). Anytime you get a pop up asking you to download something that you did not ask for, shall be killed instantly.

Now without further beating the bushes, tell us what site did that and what file did you trash so we can do some surgery.