NEW YORK — Americans clicked away on their computers and smartphones for deals on Cyber Monday, which is expected to be the biggest online shopping day in history.

Shoppers are expected to spend $1.5 billion on Cyber Monday, up 20 percent from last year, according to research firm comScore. That would not only make it the biggest online shopping day of the year, but the biggest since comScore started tracking shoppers’ online buying habits in 2001.