The Dow Jones Industrial Average, S&P 500 and Nasdaq may be hovering near all-time highs Monday, but it's not a good day for all investors. Specifically, shares of Ubiquiti Networks Inc.  (UBNT) are down on the day, falling more than 4.7%, to $50.22. On the plus side, though, UBNT stock is off its morning lows around $48.

So what's got the stock down? TheStreet's Jim Cramer pointed out that noted short-seller Andrew Left of Citron Research is calling out the company's numbers. He's basically saying that Ubiquiti's numbers aren't adding up.

In fact, Left went as far as to call Ubiquiti a fraud and something he hasn't seen in years. Left reasoned that he has facts that back up his claims, with Cramer explaining some of the numbers. In Left's view, the operating margins are out of sync vs. the industry average, while UBNT's sales per employee appear far too high. Other metrics vs. industry peers also appear lopsided.

In response to Left's claims, UBNT CEO Robert Pera had this to say, "I just put my head down and let the products and numbers speak for themselves. My apologies to those affected by these clowns."

Cramer, who manages the Action Alerts PLUS charitable trust portfolio, suggests that Pera come on the air for an interview to clear the air for investors. Left's report will be making the rounds Monday and likely throughout the week. It will hurt the stock and investors will want to hear a response from management.

So where does UBNT sit in Cramer's eyes? He acknowledges not having done enough research to discredit or support Ubiquiti, but did say he prefers Arista Networks (ANET) and Cisco Systems (CSCO) over (UBNT) stock. Ubiquiti does seem highly valued, he concluded.

While investors are being burned by the move, short-sellers are on the winning side of the equation Monday. According to S3 Analytics, short interest currently stands at $393 million, down about 1% for the year but down 31% from its highs in early August. Prior to Monday, short-sellers hadn't done too well with UBNT stock, collectively down $27 million on the year. Monday's plunge changed the narrative though, netting shorts $40 million in gains and giving them an overall profit of $13 million on the year. 

Because Pera owns roughly 70% of the float, borrowing is expensive for the shorts. Despite the hassle, bears are pressing shares lower and are betting on more downside. Because of the low supply and high borrowing fees, it should keeps shorts at bay, according to S3. In fact, only 20% of Monday's volume came from short-sellers, suggesting that investors were actually the ones walking away from the table. Still, short-sellers are looking for more downside in the near-term. 

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This article was updated from 12:11 PM ET September 18th to include data from S3 Analytics.

At the time of publication, Cramer's Action Alerts PLUS had no position in any companies mentioned.

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