Shoppers are expected to spend almost £1 billion online as retailers unleash another set of bargain deals on Cyber Monday.
Spending is predicted to soar by 31% on last year as stores offer discounts exclusively on the internet following the Black Friday weekend.
Some of Britain's biggest retailers will be hoping to avoid a repeat of problems which saw a number of their websites struggling to cope with the volume of traffic on Friday.
Cyber security expert Dave Whitelegg urged shoppers seeking bargains online to be vigilant as hackers were targeting people "all the time".
He told the Press Association: "Lots of breaches occur months after credit and debit card details have been stolen.
%VIRTUAL-ArticleSidebar-shopping-guide%"People scouting around for cheap deals may end up on scam websites. It's best to stick to reputable, well-known companies. If the price seems to good to be true, it usually is."
Some £943 million is expected to be spent online on Cyber Monday, up from £720 million last year, according to Experian-IMRG.
The amount is expected to fall short of Black Friday's predicted spending of £1.07 billion - the first time that online retail sales in the UK were thought to have surpassed £1 billion in one day.
The Centre for Retail Research said spending online and in-stores over the four-days was expected to hit £3.49 billion.
Retail giant Amazon reported record figures on Friday, with more than 7.4 million items ordered, leading to its biggest sales day ever in the UK.
But the predicted chaos on the high street failed to materialise, with shopper traffic down by 4.05% on last year, according to retail experts FootFall.
Consumer analyst Richard Hyman said: "Last year I think the industry embraced Black Friday with tremendous enthusiasm and dived in. This year it's been more muted.
"There is shopper and retailer fatigue. Everyone is saying it's going online and I think that's going to be true in some ways. But it's going to wreak the same economic damage."
Some companies struggled to keep their websites up and running on Black Friday.
The John Lewis website went down at around 3.20pm, with one IT analyst estimating the company could have lost £2.8 million.
Shoppers using the Argos, Tesco, Boots, River Island and Debenhams websites also reported problems.