The CERT/CC received reports of new malicious code known as the “W32/Nimda worm” or the “Concept Virus (CV) v.5.” in September, 2001. This new worm appeared to spread by multiple mechanisms.
It modifies web documents (e.g., .htm, .html, and .asp files) and certain executable files found on the systems it infects, and creates numerous copies of itself under various file names.
View the original CERT advisory