The days of gaudy million e-commerce spending are back, presenting the possibility that online sales have made a significant rebound from last year.

According to recent data from Comscore, "cyber-Monday" sales hit $887 million, up 5% compared to last year, and two days since then have posted sales above $800 million, the research firm reports. Comscore says the Nov. 30 sales matched "matching the heaviest online spending day on record." The notion of a record sales day in what was supposed to be a slow holiday spending season should offer the online retail industry substantial cheer. From Nov. 1 to Dec. 4, e-commerce sales rose 4% to $15.3 billion, and they've been rising even faster in recent days.

What the retail industry doesn't know yet is whether e-commerce sales are part of an improving trend for the entire industry, or if online sales are taking away from bricks-and-mortar activity. The latter would be bad news for retailers that get the huge majority of their sales through physical stores.

If e-commerce sales are taking away from store sales, it will be particularly harmful to companies that don't have large and successful online sites like Wal-Mart Stores (WMT). While Walmart store sales may be modest this year, it is by most measures the second-most visited retailer online after Amazon (AMZN).

A trend of e-commerce growth at the expense of store activity will leave retailers who have weak online traffic out in the cold.

Douglas A. McIntyre is an editor at 24/7 Wall St.