abnormal traffic, how can I avoid it?

[nomatter]

one of my site encounters very strange traffic. In this month it almost uses up the traffic limits of the hosting server (15G now). Actually the normal traffic of the website is around 100 visits per day. But now it is around 300 visits per hour! (from webstate)

The main request is Direct Request to the homepage. But actually on the homepage I have google analytics codes and google analytics shows the normal visiting numbers, around 100 per day.

The main reponse codes from the webstate are:
Code 200 - OK
Code 304 - Not Modified

I don't why such strange traffic happens. Is my website under attack? How should I avoid such situation. Any suggestions are very appreciated.
Thanks.

[bill]

You will need to look at your raw server logs and check the activity there. Log tracking software may not be giving you the clearest picture of what's going on.