How does malware work?

Question

More specifically, how does this piece of malware work? This is supposedly what was used to attack Google and other companies a few weeks ago.

I don't have any interest in making this kind of stuff, but I am interested in how it works. How do people know exactly where to target these browsers? How does someone gain access to another computer by doing this? What is actually going on? I know some of these questions are open ended, so how about an answer for the given example.

Answer 1

here's the start of a long journey, good luck
also stackoverflow has a few thigns to say

Answer 2

Someone finds a weakness in a program, and someone else writes an exploit.