A giant comet will explode in Greece on August 19th, according to Pravda, causing massive disruption of the Olympic Games. The newspaper's source is the ever-reliable Nostradamus, and a spamming net.kook:

Leading newspapers, governmental institutions, public and scientific organizations started receiving anonymous emails this week with To all people of the Earth in the subject line. The emails warn of a catastrophe which is supposedly to take place on August 13th or 14th 2004 at the Olympic Games opening. The anonymous writer refers to Nostradamus's 10th Century, Quatrain 74. The prophet predicted: The year of the great seventh number accomplished, It will appear at the time of the games of slaughter: Not far from the great millennial age, When the buried will go out from their tombs.

The spammer's date was clearly wrong, but another author has examined the prophecy in more depth and come up with the August 19th date. Just to add to the confusion, someone referring to themselves as World War Three 2003 insisted over a year ago that Nostradamus predicted:

The 2004 Athens Olympics will be canceled due to a major event to take place in late 2003 or early 2004, sometime between Nov 2003 and Feb 2004...........

Nostradamus: Giant comet to collide with planet Earth on August 19th - Pravda, 16th August 2004; Cen.8, Qua.16 Olympic Fiesole 2002-2006 - alt.prophecies.nostradamus, 6th May 2003.