NEW YORK (CNN/Money) - The stock market's two month long upswing is starting to fizzle, leading investors to wonder if maybe this was just a trader's rally and not the start of a new bull market.

Skeptics have argued that stocks have moved higher simply because short sellers are closing out bearish bets and fund managers are chasing performance in order to boost their moribund year-to-date returns. Optimists point to an improving earnings and economic outlook.

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But now there's another reason to think that this rally might be on its last legs. Corporate insiders, presumably the people who know the most about their companies, dumped shares aggressively last month. So much for a display of confidence by Corporate America. (On Monday, CNN/Money wrote about another growing fear among market bears: that earnings estimates are way too high -- click here for more.)

According to Thomson Financial, insider selling skyrocketed 125 percent in November to $2,6 billion from $1.2 billion in October. Tech insiders were especially busy as the level of selling increased to $861 million from $244 million, a whopping 250 percent rise. And insider buying? That was up just 5 percent, to $193 million from $184 million.

Kevin Schwenger, insider research analyst with Thomson Financial, stops short of calling the recent selling a bearish sign, noting that there was about $13.71 in insider selling for each $1 of insider buying last month. Schwenger says that a ratio between $10 and $20 is usually a neutral indicator for the market.

"Profit taking would be a big motivation for a lot of insiders with the market performing so badly this year," Schwenger says. He adds that one reason November might have been such a big one for selling was that many insiders were restricted from making transactions in October, since that's when most companies report their earnings.

Sell sell sell November was a big month for insider selling...especially for these tech companies. Company  # of sellers  # of shares sold  Price range of sales  Current price  Emulex  5  140,234  $23.63-$26.00  $19.75  Maxim Integrated Products  9  441,195  $31.73-$43.38  $35.54  Qualcomm  15  6,025,588  $32.95-$41.78  $39.19  TiVo  4  241,296  $6.23-$6.78  $5.55   Source:  Thomson Financial

However, last month was the first time the insider seller/buyer ratio rose above $10 since June (it was $6.41 in October) and so far in December, it does not look like the ratio will fall back below that level. According to Schwenger, there has been $231 million in insider sales through Dec. 10 and just $18 million in insider buys, leaving the insider seller/buyer ratio at about $13.

Still, James Denney, manager of the Electric City Value fund, says if you see a wave of selling, the message isn't too hard to figure out. "Usually when you see bunches of selling it tells you insiders think it's a good time to get out," Denney says. Insider trading activity is one of the key factors he looks at when evaluating stocks, and it has served him well. His fund, while down 15 percent year to date, was up 17.4 percent in 2000 and 5.4 percent last year.

Denney cautions against reading too much into a sale by one executive. But there were plenty of examples of multiple insider sales by different executives last month in the tech sector. Wireless telecom equipment company Qualcomm is particularly noteworthy. Fifteen insiders sold shares of the company in November, including CEO Irwin Jacobs, who sold 2 million shares for $70.6 million, or an average of $35.31 a share. According to Thomson Financial, this was the second-largest sale by a Qualcomm insider ever.

A Qualcomm spokeswoman said that during the company's conference call with analysts last month Jacobs mentioned that he and other insiders planned on selling shares in order to diversify assets and for estate planning purposes. The stock is up more than 40 percent since Oct. 9

Emulex is another tech company that had a fair amount of insider selling. Five insiders sold shares last month, and Thomson Financial said this was significant because it marked the first insider selling since May.

Emulex president Kirk Roller, who sold 100,000 shares, said that many Emulex executives have set plans to sell stock when shares appreciate a predetermined amount. He says this triggered many of the sales in November. Emulex, which makes host bus adapters for storage networks, has soared 137 percent during the past two months.

Insiders at semiconductor company Maxim Integrated Products also sold a sizable amount of shares last month. The stock is up more than 65 percent in the past two months. Nine Maxim insiders, including CEO John Gifford, sold more than 440,000 shares for about $14.8 million. This was the largest group sale by Maxim insiders since March, according to Thomson.

Gifford says he has sold some shares each year for the last 10 years but still owns about 3 million shares, most of which he has owned since he founded the company in 1983. He speculated that other executives might have sold in order to supplement income since executives did not receive bonuses for the most recent fiscal year (which ended in June).

And at personal television recorder developer TiVo, four insiders sold, marking the first group sale in a year. Chief technology officer James Barton sold 100,000 shares, the second-largest ever by a TiVo insider. A TiVo spokeswoman said the company does not comment on executive stock sales. Shares of TiVo have gained more than 65 percent since Oct. 9.