When UAD software is installed, UAD-2 plug-ins are copied to the following default locations:

Windows

VST (64bit)
C:\Program Files\Steinberg\VstPlugins\Universal Audio\

AAX64
C:\Program Files\Common Files\Avid\Audio\Plug-Ins\

Mac

VST
/Library/Audio/Plug-Ins/VST/Universal Audio

Audio Units
/Library/Audio/Plug-Ins/Components

AAX64
/Library/Application Support/Avid/Audio/Plug-Ins 

For default install locations for UADx plug-ins, click here.