Ever cared to look back again, when you everytime clicked on the “OK” button of this popup :




From now on, look at it once more. To check out that it isn’t malicious. And something isn’t hidden behind it.

Drive-by download is basically the “download of any malicious/unwanted object on a computer without the knowledge of user”

It is a fake webclient or you may say a fake certificate, whose sole purpose is to take control of your computer/user accounts. It may be through install of Keylogger or RAT, whatever the attacker wishes.
It’s a simple Java applet. If you’re a good programmer, you would be able to make one of those yourself.
Now a normal user will approve anything like that certificate in order to play a game, see a flash video or view a webcam.
This type of attack is by far the simplest to pull and does not rely on any particular kind of vulnerability. The Java Runtime is the only browser embeddable object which gives such a degree of access from simple Web pages. Flash, Adobe Reader, and even Signed JavaScript (disabled by default) wont allow you to do all of these, mainly because it is highly insecure!
The chances of getting success using this vulnerability is more than 90%.
If you have never seen anything like that it is a certificate shown when the security certificate is crypted.
Java in particular isn’t vulnerable and it isn’t that we should avoid all objects online using java. It is an awesome platform for web apps, the main thing here is the human factor.
The aim here is to just expose the widely used hacking methods online.
Use a good antivirus. Keep updating your browsers. Don’t run Active-X content unless you’re sure what is it.
It is just like a hidden pop-up box saying,
“Do you wanna give the whole access to the attacker”
And you click YES!!
So, before you click, think twice!!