The number of patent infringement filings shot up by 22 percent during 2011 compared with the year before, reaching the highest level ever recorded, according to a study by PricewaterhouseCoopers.

Patent infringement actions totaled 4,015 last year, marking an overall annual growth rate of 6.4 percent since 1991. The accounting firm released the results of its 2012 Patent Litigation Study on September 12.