Until about 2 weeks ago all was working fine.
Then suddenly I started receiving lots of subscribers through the plugin on my landing page. (Now I took it off.) even thought I have double opt-in enabled.
On August 16th I had 26 subscribers. Currently I have 327 subscribers, more than half confirmed. Addresses like 'gilemettehultzngx@' and 'firstname.lastname@example.org', which are 99% spambots or similar.
Any idea why this is happening and how it can be stopped?