My son is 12 and is at present in the eighth grade. I have got ample evidence that he is visiting some pornography sites secretly. His friends in the school told him about these dirty web sites and how to find them.
How I should handle this issue? We are born again Christians. This is going to ruin his life. Can you give us some idea to handle this?
I'm glad you caught this quickly. And you are correct, if the problem is not addressed soon, it will have a major detrimental impact on his life. You're going to address this issue from multiple directions at once because just one is not going to be affective enough by itself.
Make it harder to sin
First, move the computer to a public area of the house. He should not have a computer in his room at this age. Knowing that at any moment someone might look over his shoulders and see the screen will limit his viewing.
Second, every computer has the ability to limit access to certain times of the day. Set up each member of your household with their own accounts and their own passwords. Then limit your son's account to being only available when people are at home. Especially limit access during normal sleeping hours. If you don't know how to do this find a computer expert to show you how or set it up for you. I could describe it, but it depends on the system and at the moment I don't want to get bogged down in technical details.
Third, if your home has a router, you can change the dynamic name service settings (the DNS). The DNS is used to convert the address we type in for a web site into its numeric code. All Internet companies provide links to the DNS, but there is an organization called OpenDNS which provides filtered DNS resolution. You point your router to OpenDNS instead of the normally provided DNS service. Then you establish an account with OpenDNS (also free) to state what types of web sites you want blocked. You can also allow or deny specific sites if the general tables aren't accurate enough for you. If anyone accessing your router through the Internet tries to go to a blocked site, they are routed to a page that says the site is blocked instead of the actual site.
As an alternative to number two and three, you can purchase products to control the Internet access. The problem is that the product must be installed on every computer in the house your son has access to, which might not be a large problem. I have used a product called SafeEyes successfully and it has a great lock feature that prevents it from being removed without the installer's password. It will even notify you, say at work, via email any time your son even attempts to go to a forbidden site. Another product that I've heard good things about is BSafe Online. These and other products come at a cost, but they can well be worth the price.
While all of this limits his access at home, you can't be with him 100% of the time. He will have access to computers and pornography in other places, such as at school, the library, and especially at his friends' homes.
Teach him about his sexuality
The initial motivation for looking at pornography is curiosity about sex. It continues and gets worse because the body reacts to what is seen. It is evident that he is past puberty and maturing. It is time that you, or a trusted preacher or elder, needs to sit down over a series of weeks and teach him about growing up, sexuality, and what God has to say about the matter. I have written two books on the subject, one for girls and the other for boys, which have been used to teach hundreds of kids not only about growing up, but also their responsibilities as a maturing individual. See Growing Up in the Lord: A Study for Teenage Boys.
Teach him about the harm of pornography
Once he understands how and why his body reacts as it does, and that he understands what God has said about when sex is right and wrong, it is time to explain to him how pornography works and why it is harmful. I wrote an article on this, though it is geared toward older teens and adults, that you can use ("A Look at Pornography").
Almost all teens do not realize that they are being manipulated by their sexual reactions to desire pornography. It never enters their mind why pornography is available. They don't understand the industry behind it. But when they realize they are being toyed with in order to extract money from them, most teens rightly get angry. And their contempt helps them stay away from it.
It also helps them when they understand how pornography alters their view of the opposite sex because pornography treat people as sex objects. There is no personality or character; there is no love.
The above will handle most of the problem, but some children are stubborn, rebellious, or too hooked to give up just because they know it is wrong. Let it be clearly known that if he is caught with pornography he will be punished.
The best punishments are those which are associated with the problem. For instance, if he has a cell phone and you realize that he is using it for phone sex with a girl, a part of the punishment should be the loss of the phone. For examples of how to punish a child from the Scriptures see "Disciplining Children."