Noted worrywart Citron Research skewered Qihoo 360 (NYSE: QIHU) yesterday, but the leading Chinese provider of Internet and mobile security solutions is clawing back at the bear.

Calling it "the most overvalued and misunderstood Chinese Internet stock," Citron's bearish attack accuses the company of overstating its popularity when Qihoo 360 refers to itself as China's third most popular Internet company given its user base of 378 million monthly active users.

In setting a price target of $5 for Qihoo 360 that it later admits may be generous, Citron also attacks the CEO's past and the company's claims of being a legitimate player in mobile security, and argues that Qihoo 360's valuation is ridiculous when pitted against the much larger and established dot-com pioneer (Nasdaq: SOHU).

Citron will get no argument out of me on the Sohu point. I also argued that Sohu is ridiculously cheap this week.

However, after successfully nailing Chinese mobile apps specialist Sky-Mobi (Nasdaq: MOBI) -- and seeing the stock shed more than two-thirds of its value since its bearish rant -- Citron may be biting off more than it can chew here with Qihoo 360.

Qihoo 360 fired off a rebuttal last night. It doesn't necessarily address the spyware allegations of the CEO's past. And it rightfully sidesteps any valuation debates. However, Qihoo 360 effectively counters some of Citron's other knocks.

On the mobile security front, Qihoo 360 points out that its 360 Mobile Safe product has been on the market for two years and now has more than 20 million active smartphone users.

Qihoo 360 saves its best zingers for the popularity claims.

Citron's case for debunking Qihoo 360's user base stemmed primarily from the Web traffic at Qihoo's website. Citron relied on Google's (Nasdaq: GOOG) DoubleClick ad planner and's (Nasdaq: AMZN) traffic tracking to show that is certainly not the third most visited website in China. Search giant (Nasdaq: BIDU) and IM titan are the two top sites, but checks in at 21 through Google and 35 with Alexa.

Qihoo argues that its security solutions are primarily desktop applications. Its more than 370 million active users have no reason to visit its website regularly. It also claims that it doesn't use DoubleClick banner ads, so the ad planner's stats will not be accurate anyway.

Then it makes Citron look silly by pointing out that Alexa measures traffic through toolbar plug-ins running on user computers. As a security product, one of the key features of Qihoo 360 is that it erases unnecessary plug-ins. In other words, its user base will be obviously be undercounted through Alexa.

We'll see if there's a second round of the fireworks. There have been plenty of Chinese companies that have come undone as the result of stateside bearish attacks over the past year. Qihoo 360 isn't cheap by most measuring sticks, but it's also shown it's not going to be a shrinking violet if its business is inappropriately attacked.

If you want to follow the ups and downs of Citron's bearish targets, add Qihoo 360 and Sky-Mobi to My Watchlist.