A Taiwanese military website has been defaced with slogans calling for reunification with the mainland. Taiwanese Defence Ministry spokesman Huang Suey-sheng said a website operated by the ministry's Military News Agency was breached at 8pm on Monday, but declined to say whether the hacker was from the mainland. 'The data system was not damaged and normal operation of the news website was resumed at around 10.30pm,' said General Huang. An investigation has begun. The agency had noted unusual activity in the past few days and discovered on Monday night that someone had hacked into the website and changed the titles of news articles supplied by the agency to 'reunification in 2020'. The website attack caused concern for military and security authorities as it took place shortly before an exercise to be held today where jet fighters will land on a highway to simulate a dispersal drill during a mock mainland invasion. The drill, part of Taiwan's annual major war games, was due to take place as the United States was holding naval drills in the Pacific. Meanwhile, media reports in Taiwan say security officials are on alert because of 17 missing mainland visitors to the island. There is concern that the missing people could be involved in sabotage or criminal activities in Taiwan. The group came to Taiwan last Tuesday, but disappeared after they left immigration. Joseph Wu Jau-shieh, chairman of Taiwan's Mainland Affairs Council, yesterday confirmed that the group was the subject of a manhunt. 'We suspect they are related to a smuggling ring,' said Mr Wu. He declined to say whether there was a connection between the missing people and the ongoing military drills on the island.