Many trojans and backdoors now have remote administration capabilities allowing an individual to control the victim's computer. Many times, a file (often called a client or stub) must be opened on the victim's computer before the hacker can have access to it.
quotient - the ratio of two quantities to be divided. 1  proportion - the quotient obtained when the magnitude of a part is divided by the magnitude of the whole. 2  ratio - the relative magnitudes of two quantities (usually expressed as a quotient)
A difference quotient is an expression of the form [beautiful math coming... please be patient] $$\frac{f(x+h)-f(x)}h\ ,$$ which is a simplified version of: $$\frac{f(x+h)-f(x)}{(x+h)-x}$$ This expression gives the slope of the line through the points $(x,f(x))$ and $(x+h,f(x+h))$.