I have read discussions here that (if memory serves) claim the a Safari visit to Apple.Com triggers such alerts. Most websites check your browser & version with a JavaScript and alert you if the version is incapable of running their code.
The way a site knows your browser info is - your browser sends its "User Agent" info when connecting to a server - e.g., " Mozilla/5.0 (Macintosh; PPC Mac OS X 10.4; rv:31.0) Gecko/20100101 Firefox/31.0 TenFourFox/G3 " is for my browser TenFourFox(Firefox) v.31.7.
It is possible that the site's JavaScript has a flaw or the the user agent info is being sent or interpreted incorrectly. An easy way to get your user agent string is > http://whatsmyuseragent.com/ ---EDIT-URLfixed
most modern browsers have developer tools that let you "switch" what the browser "tells" a site for testing and troubleshooting... it used to be easy in older Safari, don't know about v8.0.6.