What Is "This site is Hacked by ABCD"

Hi,

Some times when i open directory or sites then a message appear on top or on full page that "THIS SITE IS HACKED BY ABCD(ABCD Can be name or email or web address)".

I saw many times but dont know what is this. How can some one hack your site and can use them according to him.

Need details about this and way of protection too.

Thanks
Jerry

Sites are hacked depending on what's running. For example, if a site is using PHP, there are a lot of PHP exploits that can be used. Sometimes it's as simple as sending a malformed URL.

Similar exploits exist for SQL & CSS. The list goes on & on. Site protection also depends on what's running & if the coder had security in mind when he wrote it.

It's mean your site is defaced by someone, they exploited your web bug, maybe using PHP injection

That would be entirely dependent on the attack used to gain access, but if you know for sure that your site has been compromised, I would think the first step is to relocate valuable information and change passwords. Secondly, try to identify how the hacker gained access to your site. You'll need a better understanding of that in order to combat it.

you need to look at how the hacker gained access, for example through whatever kind of code you are running behind the website. for example in SQL injection it can be as easy as running SQL code through a log in box which hasnt been secured to block certain things being entered.

Well, this thread is almost 2years old.
But there's nothing to lose to ask how website able being hacked via CSS? And how to prevent it?
(Ah, I sound so dummy)