Swift said she was “heartened by the love and unity” she saw from fans who “banded together” after the news broke.
“I decided that all of my energy had to go toward helping to protect the nearly half a million people I had coming to see the shows in London.
“My team and I worked hand in hand with stadium staff and British authorities every day in pursuit of that goal, and I want to thank them for everything they did for us.
“Let me be very clear: I am not going to speak about something publicly if I think doing so might provoke those who would want to harm the fans who come to my shows.
“In cases like this one, ‘silence’ is actually showing restraint, and waiting to express yourself at a time when it’s right to.
“My priority was finishing our European tour safely, and it is with great relief that I can say we did that.”
The cancelled Vienna dates formed part of the European leg of her Eras Tour, which concluded on Tuesday in London.
Swift made history as the first solo artist to perform at Wembley Stadium eight times in a single tour, a record previously held by Michael Jackson for his Bad Tour in 1988.