Last year, Web merchants had $386 million in sales on Cyber Monday, compared with $250 million on Black Friday. comScore estimates that fourth-quarter e-commerce sales will be $26.5 billion, up 24% from a year earlier. The news came as retail shares sold off Monday . Shoppers flooded stores over the holiday weekend and drove strong sales for retailers, but the steep markdowns being used to lure customers could lead to disappointments on the bottom line, Wall Street fears. The world's largest retailer, Wal-Mart ( WMT), drove heavy traffic by offering deals such as laptop computers for $398. The discount giant reported that its November same-store sales were headed for a 4.3% gain. Those results would land at the midpoint of its previous guidance for an increase of 3% to 5%. Still, given the growing popularity of Cyber Monday, perhaps people won't be so quick to cast aspersions on the first day of the workweek.