This paper presents the derivation of exact and asymptotic closed-form formulas of the secrecy outage probability (SOP) for space shift keying (SSK) systems over Rayleigh fading channels, especially in the presence of imperfect channel state information (CSI) at a legitimate receiver. Comprehensive analyses of the achievable secrecy performance limit for the SSK systems were performed by judiciously exploiting the derived SOP expressions, which enable us to obtain explicit and useful insights into the effect of channel estimation errors on the secrecy performance for the considered systems. The exactness of our theoretical analyses was validated numerically.