Options volume also soared on the speculation.
"There is a rumor circulating that Google might have an interest in CNET. Therefore, the options volume has picked up dramatically on that rumor," said William Lefkowitz, options strategist at brokerage firm vFinance Investments in New York.
Google officials declined to comment and a CNET spokeswoman was not immediately available.
Steve Weinstein, an analyst at Pacific Crest Securities, said Google's interest in CNET is "highly unlikely."
But "potentially, that could be moving the stock," he said.
Shares of CNET traded close to their year-high of $9.88, rising 5.2 percent, or 41 cents, to $8.09, on the Nasdaq on Friday.
On the options market, roughly 19,000 calls compared to 514 puts changed hands in CNET Friday morning, 31 times the normal level, according to option analytics firm Trade Alert.
February and March calls have been particularly active, giving investors the right to buy CNET shares at $10 apiece.
Investors often buy equity calls hoping to profit on anticipated share price gains and equity puts to speculate on potential price weakness.
"Option volume is active on continued speculation of a need for a partner to
CNET is also waging a battle with a consortium of activist investors led by hedge fund Jana Partners, which has sought to expand the San Francisco-based company's board and nominate its own directors in a bid to boost its share price.
CNET has rejected the proposal so far.
"Another scenario is that these rumors have originated with call buyers who took a hit after CNET issued lackluster guidance this week and were left holding the bag," said Rebecca Engmann Darst, equity options analyst at Interactive Brokers Group.
Earlier this week, CNET posted higher fourth-quarter profit but said it expects to post a first-quarter operating loss.
Google shares were up 1.5 percent, or $7.70, to $512.65.