http://www.perlmonks.org?node_id=661528


in reply to Re^3: How to deal with malformed utf8 from XML parsing
in thread How to deal with malformed utf8 from XML parsing

Well today was definitely a fruitful day. I learned about C0/C1 control codes which were the reason for google to complain. I also realized where this stuff actually comes from (someone pasting a mis-encoded chunk of text into a browser window). Finally I know not to use is_utf8 anymore :)
Thank you for your comments.

P.S.How I ended up fixing this:
$_ =~ s/[\x{80}-\x{9F}]/\x{FFFD}/g;