malechh actually referred to a tribe from a country neighbouring India somewhere around Nepal if i remember correctly who did not follow the sanatan dharm old name of Hinduism The came to be used for non hindus and non sikhs though not necessarily as a derogatory term It however does crop up in the litterature of Hindu Right Wing Sangh Parivar as generic term for Non Hindus And of course you will also find in anti indian anti hindu sites too google for more proof