You Have No Honor — Ray Jay Perreault

Book 3 in the Virus/Earth Series; End of Epoch 1
Earth was attacked by a suspicious virus (Bk1), the remaining survivors deal with the loss (Bk2), then face the attackers (Bk3) and begin to explore the universe (Bk4).
Earth is under attack and losing. The evil computer Julius takes steps to remove the threats to its existence, SIMPOC, and the remaining humans take a desperate step to control Julius and face their attackers.