当过滤器开始阻拦从嫌疑网络地址发来的邮件，发送者开始在其中放入僵尸网络（劫持电脑的网络）。
When filters blocked mail from suspect network addresses, the spammers used botnets (networks of hijacked computers) instead.
第五章和第六章分别在第四章所实现的基本数据通路的基础上实现了一些安全特性，它们是包过滤和网络地址转换(NAT)。
Chapter 5 and chapter 6 implements some security functions based on the basic data path implemented in the chapter 4, they are packet filtering and network address transition (NAT).
第五章和第六章分别在第四章所实现的基本数据通路的基础上实现了一些安全特性，它们是包过滤和网络地址转换(NAT)。
Chapter 5 and chapter 6 implements some security functions based on the basic data path implemented in the chapter 4, they are packet filtering and network address transition (NAT).
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