Which is incorrect among the following statements about the security of network information?

A、Theinformationsystemunderthenetworkenvironmentismorecomplexthanthestand-alonesystem,andtheinformationsecurityproblemismoredifficulttobeguaranteedthanthestand-alonesystem.;
B、E-mailisameansofcommunicationbetweenindividuals.Itisprivateanddoesnotusefloppydisks.Itwillnotinfectcomputerviruses.;
C、Firewallisoneoftheeffectivemeasurestoprotectinternalnetworkfromexternalattacks.;
D、Thecoreofnetworksecurityisthesecurityoftheoperatingsystem,whichinvolvestheprotectionofinformationinthestateofstorageandprocessing.