What would cause a massive spike in traffic?

[juggernaut]

Ok this is not the normal request that you might think the subject contains. Heres the issue. When I role over to the new day my script is set to run and rescan all the logs for that day. It runs at 1am. Well for yesterday 07/05/05 traffic is up 300%. I dont get a ton of traffic. It has been on the steady increase. But nothing that crazy or fast. We have been doing an ad campain but nothing along those lines has been commming from the place. We did have an issue where one of the banners was not placed on a site for a few days and that issue got fixed durring the afternoon. But I personnaly dont think that could be the source. anyway what should i be looking for to debug this? Thanks Jugg