By default in Windows Firewall, most (not all) outbound filtering is turned off
(outbound connections are allowed
) and inbound filtering is turned on
(inbound connections are blocked/not allowed
This is what Microsoft has to say:
Matt Parretta, a former spokesperson for Microsoft's PR agency, Waggener Edstrom, offered this defense: "If we turned on outbound filtering by default for consumers, it forces the user to make a trust decision for every application they run which touches the network....they will be prompted on the first launch of every application that touches the network: Instant Messaging, IE, e-mail, Windows Media, iTunes, every self-updating app such as Adobe, and so on. Unless they click 'allow', the app will be broken and won't function properly. The out of box experience would be poor, and they would soon be desensitized to the prompts."
Although most outbound filtering is disabled, Windows Firewall does provide limited outbound filtering which users may not be aware of as it is essentially invisible.
Jason Leznek, Microsoft senior product manager, told Computerworld that outbound filtering rules "are enabled by default for core Windows services as part of Windows Service Hardening, which enables the firewall to understand specific behaviors Windows services should have, and block them if they are doing something unexpected (ie, via an exploited vulnerability). Windows Firewall also protects the computer by blocking certain outgoing messages to help prevent the computer against certain port scanning attacks."
Outbound filtering can be configured to provide an additional layer of security and it does provide corporate and business administrators control over applications (i.e. peer-to-peer file sharing) they may want to restrict. Any such applications that require outbound access must be added to the rules list by using the firewall with the Advanced Security Microsoft Management Console (MMC). Configuration may be confusing for some and there is no practical way to to configure outbound filtering to stop all unwanted outbound connections. Inbound filtering can be turned on or off and through various tabs and configuration settings.