1 EXHIBIT 11 SECURITY DYNAMICS TECHNOLOGIES, INC. AND SUBSIDIARIES COMPUTATION OF INCOME PER COMMON AND COMMON EQUIVALENT SHARE THREE MONTHS ENDED MARCH 31, 1998 AND 1999 (IN THOUSANDS, EXCEPT PER SHARE DATA) 1998 1999 --------- --------- Basic earnings per share: Net income per common share ........................... $ 0.07 $ 1.03 ========= ========= Weighted average number of shares outstanding ......... 40,665 39,737 ========= ========= Diluted earnings per share: Net income per common share ........................... $ 0.07 $ 0.97 ========= ========= Shares: Weighted average number of shares outstanding ......... 40,665 39,737 ========= ========= Effect of dilutive options ............................ 1,486 2,314 ========= ========= Adjusted weighted average number of shares outstanding .. 42,151 42,051 ========= ========= - ------------------