Security services as per ITU-T X.800 are authentication, access control, data confidentiality, data integrity and non-repudiation. Security attacks can be categorized as interruption (attack on availability), interception (attack on confidentiality), modification (attack on integrity) and fabrication (attack on authenticity).

Malicious programs like virus, worm, zombie are replication on behavior and  trapdoors, trojan horse are non replication on behavior. Logic bombs, trapdoors, trojan horse, virus need host program whereas zombie, worms are independent to do need host program.