NEW YORK (CNNMoney.com) -- Online retailers continued to post big holiday sales numbers last week, with a jumpstart from a record-setting Cyber Monday, according to data released Wednesday.
So far, more than $17.5 billion has been spent online in the first 35 days of the holiday shopping season through Dec. 5, a 12% increase over the same time last year, according to comScore, an online analytics firm.
For the week starting with Cyber Monday, four separate days topped $800 million in aggregate sales for online retailers.
Shoppers kicked off the week by spending $1.03 billion on Cyber Monday, which became the heaviest online spending day on record. That was followed by $911 million on Tuesday, $868 million on Wednesday and $850 million on Thursday.
Overall, sales for the week ended Dec. 5 were up 9% from the year-earlier period -- a little below the rate of growth for other parts of the season.
"We anticipated that the post-Cyber Monday period would experience a slight hangover after many of the retailers' most aggressive deals and promotions expired," comScore chairman Gian Fulgoni said in a statement.
Promotions such as free shipping increased in popularity this year, with each of the most recent three weeks seeing more than 50% of all transactions including the incentive.
"Without a doubt, free shipping has become a critical driver of e-commerce purchasing, with the majority of consumers indicating that they will abandon their shopping carts if they get to check-out and find that free shipping is not included," Fulgoni said.
Microsoft is making a bid to own the living room with its new entertainment device. More
Only a tiny fraction of small businesses must comply with new Obamacare rules. And most of them are already providing insurance to employees. More
The Federal Emergency Management Agency announced a series of aid programs available to tornado victims who live in one of the Oklahoma counties declared a disaster area by President Obama. More