Amazon earlier today said that tomorrow it will make "a significant announcement...that will impact the competitive landscape of online shopping." Some investors apparently linked Beyond.com to the announcement.
Later in the day, Amazon asked Business Wire, the company that distributes press releases, to kill the advisory about the press conference.
Beyond.com shares closed up 2.44 to 11.13, a gain of about 28 percent. Earlier in the day, the shares reached as high as 13.5. Amazon shares were up 13.06 to 78, a 20 percent jump.
"We don't comment on market rumors," Beyond.com spokeswoman Laura Fulda said. She also declined to comment on whether Beyond.com had any plans for a company announcement tomorrow.
Amazon spokeswoman Kay Dangaard said: "We don't comment on things that we may or may not do."
This is not the first time investors have speculated that Amazon would acquire Beyond.com. Last June, Beyond.com's shares jumped more than 30 percent on similar rumors.
Beyond.com would be an inexpensive buy, considering that its shares are trading near its 52-week low and the company has a market cap of roughly $456 million.
Beyond.com's shares reached a 52-week high of 41.31 last January.
Some analysts are skeptical that Amazon would be interested in Beyond.com.
"There's talk that Amazon will add software sales to its site and that it'll buy Beyond.com," said Alan Mak, an analyst with Argus Research. "But Amazon doesn't typically buy companies unless they are an early-stage, privately held company."
Amazon, for example, acquired Accept.com, a payment solutions provider; Bibliofind.com, which offers rare book titles; and MusicFile.com, a provider of difficult-to-find music titles, for a total of $645 million last April.
"If Amazon wants to add a software store, they will probably do it themselves," Mak said. "They already have download capability since they can do it with music."
And should Amazon add software to its sprawling e-commerce strategy, Mak said Beyond.com has little to worry about.
"Beyond.com focuses on business clients and not so much on retail customers. Amazon is more retail oriented," he said.
CNET, the publisher of News.com, holds an equity stake in Beyond.com.
Bloomberg contributed to this report.