Online retailers rang up more than $1 billion in sales this past Cyber Monday, according to data released yesterday by ComScore.

Adding up to a 16 percent gain in sales over the same day last year, Monday's cybershopping spree was the heaviest online spending day in history, said ComScore, and the first to cross the billion-dollar mark. Overall, the start of the holiday season has brought good cheer to online retailers. More than $13.5 billion was spent online from November 1 to 29, a gain of 13 percent from last year.

The growth in Cyber Monday sales was driven more by higher spending per person than by an increase in shoppers. On average, consumers spent 12 percent more than they did last year, while the number of shoppers rose just 4 percent to 9 million. But promotions and discounts on the part of retailers have also helped cook up holiday sales so far.

"The online holiday shopping season has clearly gotten off to a very strong start, which is welcome news," ComScore Chairman Gian Fulgoni said in a statement." At the same time, it's important to note that some of the early strength in consumer spending is almost certainly the result of retailers' heavier-than-normal promotional and discounting activity at this early point in the season. So, while we anticipate that there will be more billion-dollar spending days ahead as we get deeper into the season, only time will tell if overall consumer online spending remains at the elevated levels we've seen thus far."