my $hashIPs = {}; 
$hashIPs->{$ip} = { totalVulns => $ipTotalVulns, vulns => $vulns };    
$hashIPs->{$ip}->{'region'} = $region;

##</code><code>##

Or without references : 
my %hashIPs;
$hashIPs{$ip} = { totalVulns => $ipTotalVulns, vulns => $vulns };    
$hashIPs{$ip}{'region'} = $region;