Bombarded with Account Registrations

-- HikaShop version -- : 2.6.4
-- Joomla version -- : 3.6.4
-- PHP version -- : 5.6.27
-- Browser(s) name and version -- : Chrome 53.0.2785.143 (64-bit)

My site has been bombarded with account registrations, sometimes 10 - 20 per day. These seem to be robots trying to get into the site, as no orders are placed. Many of them are coming from Poland. Most have been registered as user group 'registered' however in the past week the registrations have come in to user group 'administrator.' I disabled registration and now only have guest registration on the site. However this has not slowed down the registrations with passwords coming in.

Anyone else having this issue? Any suggestions on how to deal with this?

Thank you.

Hi,

That's because the problem is not with the registration itself. The hackers must use a hole on your website to create accounts without having to go through the registration form.
The last patches of Joomla are all linked to account registration and user group/user changes:
developer.joomla.org/security-centre.html
But it might come from another extension.
The best is to secure the website has much as possible:
geekflare.com/joomla-security/