More spam due to WordPress.com API key?

After installing the WordPress.com Stats plugin (for which we need our WordPress.com API key), I experience a huge surge of spam coming to my blog; in numbers this means at least ten times as much as before. I eventually got the same when I activated Akismet a year ago.

Anyone experience the same? And most importantly, anyone knows a solution? I deactivated the WordPress.com Stats plugin for now but I’m still receiving hundreds of spam messages per day…