This paper investigates the secure transmission using movable antennas (MAs) in a scenario where a legitimate transmitter Alice sends information to a legitimate receiver Bob while facing multiple eavesdroppers. The main contributions include: (1) considering a pessimistic eavesdropping scenario where multiple eavesdroppers aim to jointly decode Alice's private information, and deriving a tight and closed-form secrecy outage probability by interpreting Rician fading as a special case of Nakagami fading and using Laguerre series approximation. (2) Minimizing the secrecy outage probability by jointly optimizing the transmit beamforming and positions of MAs at Alice. The problem is highly non-convex due to the complex incomplete gamma function in the objective. To address this, the inverse of the incomplete gamma function is approximated as a linear model, transforming the problem into a simpler one with a clear structure. (3) Developing an alternating projected gradient ascent (APGA) algorithm to solve the simplified problem, and a sub-optimal scheme using zero-forcing (ZF)-based beamforming to further reduce complexity. The proposed schemes achieve significant performance gains compared to conventional schemes based on fixed-position antennas. Numerical simulations show that MAs with careful antenna position optimization can achieve better secrecy performance, and the secrecy outage probability decreases with the length of the antenna movement region. The results demonstrate the effectiveness of MAs in improving secrecy performance under statistical channel state information.This paper investigates the secure transmission using movable antennas (MAs) in a scenario where a legitimate transmitter Alice sends information to a legitimate receiver Bob while facing multiple eavesdroppers. The main contributions include: (1) considering a pessimistic eavesdropping scenario where multiple eavesdroppers aim to jointly decode Alice's private information, and deriving a tight and closed-form secrecy outage probability by interpreting Rician fading as a special case of Nakagami fading and using Laguerre series approximation. (2) Minimizing the secrecy outage probability by jointly optimizing the transmit beamforming and positions of MAs at Alice. The problem is highly non-convex due to the complex incomplete gamma function in the objective. To address this, the inverse of the incomplete gamma function is approximated as a linear model, transforming the problem into a simpler one with a clear structure. (3) Developing an alternating projected gradient ascent (APGA) algorithm to solve the simplified problem, and a sub-optimal scheme using zero-forcing (ZF)-based beamforming to further reduce complexity. The proposed schemes achieve significant performance gains compared to conventional schemes based on fixed-position antennas. Numerical simulations show that MAs with careful antenna position optimization can achieve better secrecy performance, and the secrecy outage probability decreases with the length of the antenna movement region. The results demonstrate the effectiveness of MAs in improving secrecy performance under statistical channel state information.