A very strange thing happened to my blog and this plugin.
I installed this plugin days ago (september 13) and was walking great, but today I went to check how Spam are working, to my surprises I have found some Spam, but I didn't think about it to much.
Then in the afternoon I checked again and more SPAM found, so I search for the plugin options to see if something is wrong, to my surprise the plugin is not listed on my plugin.
I checked via ftp and there only one file on the plugin folder, everything inside was deleted.
I'm uploading the plugin again, but could be a hack or something?
http://wordpress.org/extend/plugins/si-captcha-for-wordpress/