Viral protein involved in the evasion of host innate defense by inhibiting the interferon regulatory factor-3 (IRF3) protein. Viral infection triggers the phosphorylation and activation of IRF3. The activated IRF3 migrates to the nucleus, where it complexes with the transcription coactivator CREBBP/EP300, leading to the transcriptional activation of the IFN-alpha and IFN-beta genes. Several viral proteins directly bind to IRF3 and inhibit its transcriptional activity while others target it to the proteasome for degradation.