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After showing caution last month, short sellers seemed to be prompted into action in the first two weeks of this month by the overbought markets, the political and geopolitical uncertainties and the rising concerns about a sizable market correction. Moves in the most shorted stocks traded on the Nasdaq were mostly upward between the April 28 and May 15 settlement dates.

Leading that trend was semiconductor company AMD, with a double-digit percentage rise in the number of its shares short during the period. On the other hand, bucking that trend were biotech companies Opko Health and Synergy Pharmaceuticals.

Note that still only three Nasdaq stocks had more than 100 million shares short, as of the middle of this month. However, two of them remain very far ahead of the pack.

Frontier Communications

After retreating marginally in the previous period, the number of shares short in Frontier Communications Corp. (NASDAQ: FTR) rose more than 5% to more than 270.49 million as of the most recent settlement date. That was 23.2% of the telecom’s float, as well as the 18th consecutive period with more than 200 million shares short. The daily average volume rose sharply, so the days to cover dropped from around nine to less than five.

During this latest period, Frontier finally announced the long-feared dividend cut. The share price tumbled more than 31% in the first two weeks of this month. The stock has recovered a little since then, and closed most recently at $1.37 a share. It hit a 52-week low of $1.19 at the end of the short interest period. The 52-week high of $5.30 was seen about a year ago.

Sirius XM

The more than 252.10 million Sirius XM Holdings Inc. (NASDAQ: SIRI) shares short by the middle of May was less than 1% higher than on the previous settlement date. It was only the fourth period so far this year in which the number of shares short has grown, and the most recent figure represented 16.9% of the total float. As the average daily volume plunged from a year-to-date high, the days to cover jumped from less than six to nearly 10.

Warren Buffett remains an investor in Sirius during, both directly and indirectly. The stock ended the initial two weeks of the month more than 3% lower, while the Nasdaq climbed less than 2% between the settlement dates. After hitting a 52-week high of $5.53 in March, the stock closed on Wednesday at $5.11 a share. The 52-week low of $3.74 was seen last summer.

AMD

By the middle of this month, Advanced Micro Devices Inc. (NASDAQ: AMD) had more than 146.13 million shares short. That was a gain of nearly 21% from the total on the previous settlement date. It represented 17.5% of the company’s float, and it was by far the highest level of short interest in at least a year. It would take less than two days to cover all short positions.

Analysts had mixed reactions to AMD’s most recent quarterly results. While the May 15 share price was around 14% lower than on the previous settlement date, it was down more than 24% at one point in the interval. The stock closed at $10.89 on Wednesday, about 4% lower year to date. Shares have changed hands at between $3.88 and $15.55 in the past year.

Intel

More than 98.40 million Intel Corp. (NASDAQ: INTC) shares were sold short as of the most recent settlement date. Short interest increased more than 8% during the period to total 2.1% of the company’s float. Note that it was the fifth period in a row with more than 90 million shares short. As of mid-month, it would take more than four days to cover all short positions.

Big spending on the cloud is seen as benefiting Intel. Though the stock ended the short interest period more than 1% lower, that was after being up more than 2% at one point. The most recent close at $36.22 a share compares to a 52-week trading range of $30.13 and $38.45 and is about 21% lower than at the beginning of the year.

Opko Health

Opko Health Inc.’s (NASDAQ: OPK) short interest of more than 74.04 million shares on the most recent settlement date was fractionally lower than in the previous period. That is around the same number shares of short in each period since early in the year, and it was 22.2% of the total float. The daily average volume rose from a year-to-date low, and the days to cover retreated from a year-to-date high of about 23 to around 14.

For well more than a year, the CEO frequently has bought batches of Opko shares. The stock closed most recently at $6.44 a share, in a 52-week trading range of $6.37 to $12.15. The share price ended the two-week short-interest period down more than 12%, and it has retreated further since then. The stock is now more than 30% lower since the beginning of the year.

Yahoo

Short interest at Yahoo! Inc. (NASDAQ: YHOO) totaled more than 63.70 million shares on May 15, which was up more than 7% from the prior settlement date. That was the highest level of short interest in at least a year, and it was also 7.2% of the total float. The days to cover grew from around seven to more than eight during the period.

This internet portal pioneer is in the process of being acquired by Verizon. Short sellers watched its stock rise more than 3% during those two weeks and a little more afterward. The most recent closing share price was $50.32, which is down around 30% year to date. In the past year, the shares have traded between $35.05 and $51.23 apiece.

And Others

Rounding out the top 10 were Comcast Corp. (NASDAQ: CMCSA), Novavax Inc. (NASDAQ: NVAX), Synergy Pharmaceuticals Inc. (NASDAQ: SGYP) and Apple Inc. (NASDAQ: AAPL). Synergy saw a more than 20% drop in its short interest between the latest settlement dates. The leading gainer among these four was Apple, with about a 10% rise in the number of shares short.

Lingering just outside the spotlight of the top 10 most shorted Nasdaq stocks were Oclaro Inc. (NASDAQ: OCLR), Micron Technology Inc. (NASDAQ: MU) and BlackBerry Ltd. (NASDAQ: BBRY).