CNET said a representative from the group - which calls itself 'w0rm' - informed it about the hack via a Twitter conversation.
A spokeswoman for CBS Interactive - the owner of CNET - said the firm had "identified the issue and resolved it".
According to CNET, w0rm offered to sell the database for 1 Bitcoin, or $622.
But it added that the hacking group said the plan to sell the database was to gain attention and "nothing more".Improve security?
The representative of the group claimed that it hacked CNET servers to improve the overall security on the internet.
The group has claimed to have successfully hacked the BBC last year, as well as websites of Adobe and Bank of America.
It says that by targeting high-profile websites it can raise awareness of security issues.
"[W]e are driven to make the Internet a better and safer [place] rather than a desire to protect copyright," the representative said in a Twitter exchange with CNET.
On Monday, the representative offered a security solution to CNET by tweeting: "#CNET I have good protection system for u, ping me".
According to CNET, 27.1 million unique users visited its desktop and mobile sites in the US in June this year.