A 26-year-old male farmer is admitted with fever and cough for 2 weeks, and epistaxis, gingival bleeding, and extensive ecchymoses for 3 days. Physical exam: moderate anemic appearance, marked tenderness over the mid-sternum, spleen palpable 1 cm below the costal margin, and large ecchymoses on the arms and buttocks. Laboratory tests: Hb 72g/L, WBC 3.8×10<sup>9</sup>/L, PLT 34×10<sup>9</sup>/L, prothrombin time 16 sec (normal control 12 sec), fibrinogen 1.2g/L, urine RBC (++). The most likely cause of bleeding in this case is: