Hi guys !
Already thanks for your advises.
The users are from many different locations in Europe. So it's not related to one single computer using multiple accounts.
It's not clear for me when it started. I think it just became noticeable when more users were using the site.
I can't related it with some plugins, neither with a version of Oxwall. I'm using version 1.7.3 now but the problem was also visible when I was using 1.7.2.
I'm using the Google Plus theme now. But the problem also there when I used the Crayon theme.
Apart from some small CSS changes, I only changed some custom code for the IP tracking. I'm using Varnish caching, so I had to change the IP by the X-Forwarded-For IP address, otherwise I would see all users coming from the address 192.168.3.104 (which is my Varnish server). I have also tried to set the Varnish server in passthrough mode (for not caching anything) but the symptom still returned.
The following purchased 3rd party plugins are being used :
- Affiliates
- Country Flag
- Link Track
I added some some modules after I had already seen the symptoms.
I had already disabled "Link track" but that didn't rule out the problem
I'll with disabling the "Affiliatates" plugin after announcing that to the users.
Disabling the "Country Flag" plugin is not possible as this information is necessary for the information in the profiles.
My site was not moved from another location. It's still the first installation, but just upgraded from 1.7.2 to 1.7.3.