Four people were arrested by Abu Dhabi authorities on charges of "tribal instigation and libel'' through posts on social networking site Twitter, UAE media reported Monday. The three Emirati men and a Palestinian woman will remain in custody for seven days pending investigation. The arrests stem from insults being traded in a "heated discussion'' between the Palestinian woman and the three Emirati men via the website last month. "Some people do not understand the grave consequences of their conducts on social networking sites or over the Internet in general,'' UAE’s al-Bayan daily reported, quoting an unidentified official from the office of Abu Dhabi Attorney General.