This is a leech. I found it and here is the link.
Put the class files in minecraft.jar and delete meta inf.
Also, not sure if this requires modloader but you can find the current version of it on minecraftforums or something.
Here is a screenshot
Virus Scan http://virusscan.jotti.org/en/scanresult/07193563fa59b00b0b5228386c473642cc42de25
