Dora Is Examining Her Log Files and Notices Several Access

Dora is examining her log files and notices several access attempts with the following string:
GET/default.ida?NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN%u9090%u688%ucbd3%u7801%u9090%u6858%ucbd3%u7801%u9090%u6858%ucbd3%u7801%u9090%u900%u8190%u00c3%u0003%u8b00%u531b%u5 3ff%u0078%u0000%u00=a HTTP/1.0
She opens a browser to visit her own website and notices the front page had been defaced to say the following:
"HELLO! Welcome to http://www.worm.com! Hacked By Chinese!"
What may have happened?

A) Code Red got to her web server
B) An attacker used a fuzzer to overflow the query string
C) Class case of Michelangelo
D) The Nachi worm found her site and successfully exploited it.