It seems the groups plugin is an easy bite for the spammer

Why do All the spammers prefer using the groups to spam just after signed up? They mostly create groups which has long meaningless words, with(out) a few pictures in, which seem as if they are created automatically, by a bot. I can't understand this, but they do. Could  a reCaptcha plugin, on the process of creating groups, prevent us from those  spammers? Does anyone work on such a captcha project for elgg groups plugin? or Any idea?