The Register: "To alert users of the presence of a Trojan or privacy threatening program running on
their systems, personal firewalls have been adapted so they monitor and block
outbound traffic (as well as blocking inbound network traffic).
If a malicious program becomes active a user will be alerted and the application will
be blocked by a personal firewall (unless a user is daft enough to agree that it
should be able to access the Internet, of course)."