Ursula sister, I am just a newbie here, and have just stepped into this CSS world lately, so I don’t deserve to be called “Sir” as my knowledge is very little. In fact I consider both of you my teacher, and have learned a lot from you, because of the contribution you made to the forum. I hold you members in high esteem because of enormous knowledge you have.

Now let’s come to the query being asked by you, but in order to comprehend the concept of how a bug can affect a computer system, it is required to first understand the a few basics, that how a combination of both software and hardware work together to perform a task.

Basically digital computers which we use normally, operate on bits, and bit is smallest unit of information. Bit can either be 0(zero) or 1(not literally). Zero is considered as an off signal, and 1 is considered as an ON signal. For our own ease, the convention was set by the pioneers that 0 and 1 would represent OFF and ON signal. For example if you write “A” in computer’s notepad, then how computer understands it is something like “01000001”. 8 bits can represent any character. So these bits are flowing through circuits which a hardware of computer is composed of, and bits are basically signals which instruct/tell hardware that what action is to be performed.

Software contains a set of instructions which tells exactly what a hardware has to perform. Instructions are composed of bits (combination of 0s and 1s), which are signals for a hardware. Hardware understands those signals and perform accordingly. And software programs which programmers write may seem like an amalgamation of math and some English, to ordinary people. These programs are then converted into binary form, which is 0 and 1, which a computer hardware understands accurately.

Now I give you my explanation regarding why Facebook was affected by that bug. A bug is basically a flaw in a software program, which produces unintended results. It is a mistake made by a programmer while writing a program. As you know Facebook is the biggest social media web application, which is expanded over hundreds of thousands of computers, which work together to serve billions of users’ requests daily. So to instruct these thousands of computers, there are thousands of different developers who develop software programs for that purpose. So many different developers are working on many different pieces of the bigger software system, and all these pieces fit together to perform a specific task. So imagine that there are billions of billions of lines of code which is responsible for delivering such a service to billions of users. And programming is done by a programmer which is a human, and human make mistakes, but in software industry, sometimes it is common practice that programmers tend to make mistakes normally, and it’s inevitable, because of the nature of the work. E.g.,

If ( isThereEmergency == True)
{
Find_Affected_Area
Notify_Affected_Area_People
}
Else
{
No_Action
}

Let us assume that if Find_Affected_Area code has some bug then it would not produce desired results.