The H_∞ filtering for event-triggered discrete-time switched systems subject to denial-of-service (DoS) attacks is considered. Based on the event-triggering scheme, the switching signal and the measured output signal are sent to remote switched filters through networks susceptible to malicious attacks, which may cause the filter mode mismatched with the system mode. Taking the asynchronous switching into account, we give a switching law with the average dwell time (ADT) guaranteeing the exponential stability with the H_∞ performance of the event-triggered switched filtering error system (SFES) in the absence of attacks by employing the multiple Lyapunov function (MLF) method. Then, under the given ADT, sufficient conditions on the attack duty cycle are proposed in the form of linear matrix inequalities (LMIs) to ensure that the event-triggered SFES under attacks is still exponentially stable, and the relation between the H_∞ performance index and attacks is quantitatively proposed. We give an example on the boost converter to show the effectivity of the results.