Over two million of the overall number of POWs held in Russia during World War I (2.4 million) were soldiers of the Austro-Hungarian army.
Up to 200 000 of those spent years not in European Russia or Siberia which has become the synonym of captivity in Russia but were sent to Russian Turkistan, i.e. the General Gouvernement Turkestan which comprised the territory of now independent states Uzbekistan, Kyrgyzstan, Tajikistan, Turkmenistan and the Southern part of Kazakhstan.
For a concise overview of WWI captiivity in Russia see:
International Encyclopedia of the First World War
Prisoners of War (Russian Empire)
by Reinhard Nachtigal and Lena Radauer
http://encyclopedia.1914-1918-online.net/article/prisoners_of_war_russian_empire