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Most routers have only a one-way firewall providing only inbound protection unless the router specifically states that it has a 2-way firewall. Two-way firewalls provides both inbound and outbound protection.
Some will tell you that you do not need outbound protection when you are behind a router. But without outbound protection, your computer is vulnerable to malware, or even non-malware, that can call home to install malware on your computer that can cause you too many problems. As has been noted by many examples on this forum, not all malware comes from the internet. These can come from cd's, dvd's, usb drives, etc.
So, outbound protection is surely needed and most routers do not have this.
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