There are many different visitor counters and they all have different requirements as to how they count for a visit. FullTraffic's counter increase by an increment of 1 every time your website is shown to the visitor. Other third party counters may require 30 seconds of browsing in your site, one or more clicks, etc. There may also be a time lag between the visits and the count of that visit. For instance, your counter may update once every 3 hours, 8 hours or 12 hours, while the visitors are still being sent.
Furthermore, if your hosting is not prepared to receive a large amount of visitors in a short period of time, it may cause your hosting to overload and crash. While your site is down we continue sending visitors which will not be counted by your counter. For further information, please send as an email.