since I installed 2.8 beta 1 64-bit version, my ZoneAlarm Security Alert pops up with warnings about Renoise Plugin Server is trying to access the Internet
AudioPluginServer32.exe and AudioPluginServer64.exe (and similar names on other platforms) are new additions to Renoise 2.8 that allow us to use bridged plugins. This is what enables the use of 32-bit plugins within 64-bit Renoise, and vice versa. You can be sure these processes are harmless (as harmless as Renoise itself, anyway).
The fact that some of your VST plugins are trying to go online is really nothing that we can control. This was probably already happening in older versions of Renoise, ie. the plugins also tried to get online from the Renoise.exe process. You have probably already white-listed Renoise in the past, or maybe ZoneAlarm already knew about Renoise and has an exception built in for it.
If you want to know exactly why your reFX plugins are going online, then you should contact reFX support to find out. My guess it that the plugins are “phoning home” to check for updated versions, or possibly as part of their copy protection.