We've looked through the posts related to spam and decided to sum up the antispam solutions, you can take advantage of:

1. Antispam plug-ins, for example, Watchdog plug-in

2. IP Tracker – so you could find out the IP range of spammers and block it. You can do that in the Cpanel of your hosting server. Also CloudFlare has the option (in the Threat Control area) to ban IP ranges.

3. User roles – change the user roles, so that the new users can't post. The negative side of this action, you'll have to change the roles of each member to normal later.

4. If your website, oriented to some specific country, you're free to block the IP s of undesired countries.

5. Adding required custom sign-up questions – this will cause additional troubles for the spam software to make verification post to the database with sign-up section. You can add such a question here: Admin Panel>>Users>>Profile Questions>>Add Question.

If none of this works, there's an opportunity that these profiles were created manually by real person(s). We can suggest using the Mandatory approve feature, that will decrease the spammers' activity. You should simply go to Admin Area > Privacy & Permissions and check the 'Mandatory user approve' box. In this case you will have to approve users before they get an access to the site.