I set the Unique IP Access Restrictions to "100" IPs, cause in Germany there is nearly noone, that has a static ip.
The standard of these setting is 5 IPs every 30days. If your users login every day you need more than 30 allowed IPs. If somone uses an iphone, a mobile computer and a desktop computer, he may use 3 IPs a day
You can't prevent account sharing in general without restricting the Ips, but you can prevent linksharing with s2member and its levels.
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