Terrorist attacks in Moscow and in general.

There were explosions in Moscow today again, this time at three metro stations. Everything had been calm for several years, and we had already settled into a peaceful life, but now this has happened again. In this connection, I would like to ask how you feel about it? Of course, negatively, but I would like to hear your thoughts on this, as the topic is, as it turns out, very relevant and a source of concern for many.
P.S. I know that I am posting this in the off-topic section, but I ask that you do not engage in irrelevant discussions; this is a serious question.