After reviewing the javascript and the disassembled Java app this is how it works. The javascript links to a Java app that runs on the computer and runs various tasks. I didn't see any code that minds performance but disassembled code is really hard to read. I distinctly recognized a SHA1 hashing function which makes sense because assisting in rainbow tables is a way to get bitcoins. I don't think that there is a virus in there or anything but it's still unethical to use your user's processor like that.