Read the following article and answer the question.

While there are other things on my mind today , it is hard for me to ignore the fact that today is September 11th and that I used to work for Cantor Fitzgerald Securities and spent June 1993 thru June 1996 working on the 32nd and 104th floors at One World Trade Center . There were plenty of times when I was at my desk at 8:47 AM and never did we ever expect to have a plane come thru the windows . I still have a hard time thinking about the people , their families and everyone who went to work on 9/11/01 just like any other regular day in their life , not knowing how everything would change , in some cases forever , afterwards .

What event is the narrator referring to for most of the passage ?
a terrorist attack