I Q  If I am on a website such as Facebook or Youtube and see some people talking badly about a Shia brother, am I obligated to post something to defend him? Or is it only recommended? It is better to defend the said person if it is considered as defeating oppression or propagating the true religion.
Q  Is it permissible to visit pornographic sites?
If it involves sexual enjoyment then it is prohibited.
Q  We know that replying to the greeting if it was in the form of Salam is obligatory. Is it obligatory to reply to it if it was in an internet group or chat room?
It is not obligatory.
Q  Is playing online games like “pool”, without money, with opponents, is prohibited or disliked or permissible?
It is permissible.
Q  Please elaborate on question 18 in the following link in your site
I use cafés to do college work sometimes and it is a public place where anyone is allowed to go on any website except those with pornographic material and so on. What about the library at college?
As long as it is not considered as encouragement to the prohibitions, it is permissible to enter the café and the library and use them.
Q  When it comes to today’s way of interacting online, there is something called “smilies” or “emoticons” which show what the person’s expression is. Is it permissible for a boy and a girl to communicate through the internet messenger this way?
If the said involves sexual arousal or sexual lust then it is prohibited. Otherwise, it is permissible.