How to resolve "Security Warning: Untrusted VPN Server Certificate!" warning on Linux systems when running the AnyConnect VPN client:
Solution:
# cd into hidden '.cisco' directory:
$ cd /opt/.cisco/certificates
# rename ca directory
$ sudo mv ca ca.orig
# link system certificate directory to ca
$ sudo ln -sf /etc/ssl/certs/ ca
# restart vpn service
$ sudo /etc/init.d/vpnagentd restart
Source: GT FAQ