Some Islamic sites have proved that Imam Mehdi has already come. Please review the site content and advise us.

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. After having visited the site you mentioned, we found out that it is pervert and corrupt. It does not follow the path of the Salaf (rightly guided predecessors). So, we advise you dear brother to stay away from such sites. As for al-Mahdi, he is not Muhammad Ibn al-Hassan, he is Muhammad Ibn Abdullah. His emergence is one of the Signs of the Day of Judgement. But nobody knows when he will emerge or whether he was already born. All such knowledge is with Allah Alone. Indeed, Allah predestines it and executes it when and how He wishes. So many people through out Islam history claimed to be al-Mahdi . But, they always ended up disclosing their proper reality which is nothing but trying to deceive people. Allah knows best.