Hi, welcome to the forums.

You could start by doing a google search for your post’s Subject ‘classloader virus’ this returns many hits, this is just one of them http://www.f-secure.com/v-descs/classloader.shtml.

Reading some of them will give you an idea why you are being infected.

You need to ensure that you have the latest versions of Java or Java Virtual Machine if installed.

Read How did I get infected in the first place and follow Tony’s advice. He will tell you about some ways to make your computer more secure and link to some excellent free tools to help with that.

If you allow Java by default it can be as simple a website that runs a java applet on your machine and because it is an accepted download nothing gets stopped.