By the Numbers

Stocks investors are shorting the most

Traders on the floor of the New York Stock Exchange on Monday
Getty Images

After a temporary drop in the last six weeks of 2013, short interest is back on the rise.

The NYSE reported on Monday that short interest rose to 13.8 billion shares in the first half of January from 13.41 billion on December 30, a 2.98 percent increase – the biggest such bi-weekly increase since mid-June of last year.

Likewise, Nasdaq also showed a modest increase of 0.5 percent in short interest during the same period. As of mid-January, short interest rose to about 7.62 billion shares, compared with 7.58 billion shares as of December 31.

(Read more: Betting against Apple? Not so fast: Ex-CEO Sculley)

Short interest measures the total number of shares of a security that has been sold short, expressed as a percent of total tradable shares.

Investors track short-interest levels to gain a sense of where a stock might be headed, along with some insight into whether any positive news might force short traders to cover their positions, pushing stocks higher.

Cliffs Natural Resources, U.S. Steel, Lennar and D.R. Horton, for example, have some of the highest ratios in the S&P 500 index, with more than 18 percent of their float sold short.

Here is a look at the most heavily shorted stocks:

Most shorted stocks in the S&P 500

Ticker Company Price YTD % Chg. Short Interest
CLFCliffs Natural Resources Inc.$20.92 -20.234
GMEGameStop Corp. Class A$36.95 -2525.1
XUnited States Steel Corporation$25.70 -12.922.7
ADTThe ADT Corporation$38.14 -5.820.4
FTRFrontier Communications Corporation Class B$4.93 5.919.8
JOYJoy Global Inc.$53.73 -8.119.7
LENLennar Corporation Class A$38.99 -1.419.4
CVCCablevision Systems Corporation Class A$16.43 -8.418.7
DHID.R. Horton, Inc.$22.95 2.818
TRIPTripAdvisor, Inc.$77.96 -5.917.7
VRSNVeriSign, Inc.$59.92 0.216.8
FSLRFirst Solar, Inc.$50.10 -8.316.5
DGXQuest Diagnostics Incorporated$53.35 -0.415.7
WINWindstream Holdings, Inc.$7.52 -5.814.6
PBIPitney Bowes Inc.$21.74 -6.713.9
GRMNGarmin Ltd.$45.68 -1.113.6
TSNTyson Foods, Inc. Class A$34.92 4.413.5
HASHasbro, Inc.$51.77 -5.912.1
EAElectronic Arts Inc.$24.57 7.111.7
EXPEExpedia, Inc.$66.80 -4.111.4

—By CNBC's Giovanny Moreano. Follow him on Twitter: @giovannymoreano