Prisoners were held at Verdala Barracks, Polverista Barracks, St.Clement Camp & Fort Salvatore. These were guarded by the Royal Malta Artillery & King's Own Malta Regiment of Militia. In the middle of 1916 prisoners numbered 1,670 from Germany, Austria, Bulgaria, Egypt, Turkey & Greece.
At the start prisoner restrictions were relaxed with reports of some being allowed to visit Valletta. However, thing tightened up following the escape of Ensign Fikentscher & an Austrian civilian internee. Also, prisoners were able to report on ship movements in the harbour & get messages out of the country. This led to all windows with a view to the harbour being blocked off.
Some notable prisoners held on Malta during WWI were the crew of the Emden. A German surface raider responsible for sinking many allied ships. One of the officers was Lieutenant Franz Josef, (Prince) Von Hohenzollern of the German Royal Family.
Another officer was Karl Doenitz who was later to become Grossadmiral, Commander in Cheif of the Kriegsmarine. He took over after Hitler's suicide. Doenitz was in command of the submarine UB 68 which developed a technical fault & had to surface. It was attacked by the escort sloop Snapdragon off Gozo & Doenitz & the crew were forced to surrender. Some stayed behind to scuttle the submarine to avoid capture & went down with the ship.
General Liman Von Sanders was also held. He was commander of the Turkish Army on the southern front in Syriah & head of the German Military Mission sent to Turkey in 1914.
Their are reports that Rudolf Hess was also held but many authors consider this questionable
The prisoners published their own newsletter called Camp-Nachrichten.

Verdala Barracks were used for Italian prisoners of war in WWII.

MV Highland Chieftan - Photo courtesy of Les Hutton

The MV Highland Chieftan was used to ferry Italian prisoners of war captured by the 8th Army from Algiers to Malta. The above photo was taken before the gun was mounted.

Italian POW's on Malta

Malta Family History - http://website.lineone.net/~remosliema/Italian%20and%20German.htm This site contains material & photos plus lists of names of prisoners.