Condemning People on Internet
Question

                I am 22 years old and I am from XXXXXX .

In the former Soviet Union Islam is reviving, but many Muslims still do not have much knowledge about religion. There are some Russian-language Islamic web-sites in the Internet and they host discussion rooms and view forums for Internet users. Sometimes a Muslim participant might say something, which is absolutely not right in Islam and he/she might not know it because he/she might lack some knowledge. 

My brother in XXXXXX  participates in these discussion rooms (view forums) and he asked me to ask you a question, which is as follows: 

"... There are some discussion rooms and view forums on the Internet where participants can express their opinions and tell their thoughts on different issues on Islam. 

Sometimes a Muslim participant might disagree with certain thoughts of another Muslim participant and criticize his/her opinion or expression. However, sometimes such a critique might touch the participant’s personality and [also] his/her way of belief, i.e.aqeedah. 

When somebody is criticizing his/her brother/sister Muslim in such a manner, the latter might not be present in a discussion room and he/she might never come back to see it again. [In my country we have rare access to Internet. This means that somebody might never see the view forum again, hence he/she will never see the answer to his/her thoughts]. However, certainly, this critique becomes known to other participants of the discussion room. 

Is such a critique considered backbiting/slander, i.e. ghibah, because of the fact that the one criticizing is not aware of whether the one criticized knows it? Might it be so that a Muslim talks about another Muslim such things, which the latter one would not want to be talked about him/herself behind his/her back. 

As you understand the question is important, because I was criticizing some thoughts of some Muslims too. 

If it was ghibah, then I will have to make repentance and to ask those Muslims to forgive me and never do it again ..."
Praise be to Allah.Gheebah (backbiting, 
    gossip) means that you mention something about your Muslim brother which he 
    does not like, such as his faults. This is haram (impermissible), no matter 
    by what means it happens or whatever form it takes. It is haram according to 
    the consensus of the Muslim scholars. Criticizing people, if the aim is to 
    expose their faults, is gheebah and is among the “evil uttered in public” 
    that Allah does not like [4:148]. But if the intention is to put people off 
    a person’s evil action that is forbidden according to sharee’ah (Islamic 
    law), to cause a person to stop doing that, to combat someone’s bid’ah 
    (innovation) and warn people against it, or to expose something false that a 
    person has said in front of others in discussion groups or newsgroups on the 
    internet or elsewhere, then this is permissible and is not the gheebah which 
    is forbidden. Indeed it is an act of worship that brings a person closer to 
    Allah, or it is an obligation upon whoever is able to do that. The salaf 
    (pious predecessors) condemned innovators and critiqued the narrators of 
    reports, in sincerity to Allah and His Messenger (peace and blessings of 
    Allah be upon him). What is important is to look at the aim and intention.
    
And Allah knows best.