The easiest way to block comment SPAM is to turn of comments altogether. Another way is to turn of comments to existing posts periodicly which is the way I do it (using a cron job). I'm running Pebble for my blog so disabling comments and trackbacks in bulk is easy using Perl and regular expressions:
perl -pi -e 's/\<commentsEnabled\>true/\<commentsEnabled\>false/' `find . -name [0-9]*.xml` perl -pi -e 's/\<trackBacksEnabled\>true/\<trackBacksEnabled\>false/' `find . -name [0-9]*.xml`This is the same approach as I have been used previously to rename categories.