Just to add a little info, the Maltese Casino was a modified, already existent, virus. I examined the innards and saw that the date check code was very clumsy although it did work. It was nowhere near as elegantly written as the rest of the .com file. However it served as a good detection string.
Strangely enough the 15th August is a national holiday in Malta - a big one - where we literally celebrate not becoming part of Germany during WW2. Malta was out of food and aviation fuel. Fighters could not take off. The Ohio made it into harbour and fuel was trucked straight to the waiting planes!
Anyway, the point is that the writer set his code to trigger on a day when the fewest computers would have been turned on. Most businesses would be on Summer shutdown and everybody would be at the beach!