Some clients of TPNQM SA were redirected to a malicious site when they tried to access the TPNQM main site. Bob, a system administrator at TPNQM SA, found that they were victims of DNS Cache Poisoning.
What should Bob recommend to deal with such a threat?

A. The use of security agents in clients' computers
B. The use of DNSSEC
C. The use of double-factor authentication
D. Client awareness