Samsung Electronics Co. was ranked fifth in the number of lawsuits filed against it by non-practicing entities last year, down two notches from 2012, as the so-called patent trolls shifted focused to U.S. mobile carriers, data showed Monday.

In a sign of intensifying battle over copyright infringement, the South Korean tech giant had 38 cases filed against it in 2013, ranking fifth in the number of patent suits filed against tech firms by NPEs, the data by U.S.-based market researcher Patent Freedom showed.

Patent Freedom defines NPEs as entities that earn or seek to earn the majority of their revenue from licensing or enforcing patents.

Despite having one more patent suit filed against it than the year before, Samsung's ranking moved down from third place tallied in 2012, when NPEs filed 37 lawsuits against the world's No. 1 smartphone maker.

Market watchers said the relative decline in the rank apparently reflected a change of target by NPEs that turned to U.S. mobile carriers last year.

U.S. telecommunications firm AT&T Inc. topped the list with 51 patent rows with NPEs, up five notches from a year earlier when it was embroiled in 24 lawsuits. Google Inc. and Apple Inc. followed with 42 cases each.

Verizon Wireless, another U.S. mobile carrier, ranked fourth on the list with 42 patent rows, compared with 25 cases tallied last year.

Samsung's smaller rival LG Electronics Inc., meanwhile, ranked 14th on the list with 27 lawsuits, down nine notches from a year earlier despite the number of cases increasing by two.

NPEs filed a total of 3,134 patent lawsuits against global technology firms in 2013, up 18 percent from 2,652 cases tallied a year earlier, the data also showed.

For the past five years, Google was the biggest target, with 192 cases, followed by Apple at 191 cases and Samsung with 151 cases. LG Electronics ranked 10th with 116 rows over the cited period. (Yonhap News)