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While hackers with motives make headlines, they represent less than 20% of all net- work security breaches. More common are instances of authorized users accidentally winding up where they should not be and inadvertently deleting or changing data. However, the Internet introduces another concern: some Internet surfers are bound to go where they have no business and, in so doing, threaten to wipe out data to which they should not have access. Before picking a firewall, companies need to adopt security policies. A security policy states who or what is allowed to connect to whom or what. You can group all users by department or classification. The better firewall products let you drag and drop groups in a graphical user interface (GUI) environment to define network security easily. Two methods are most often used together to establish an Internet firewall. They are application and circuit gateways, as well as packet filtering. With application and circuit gateways, all packets are addressed to a user-level application on a gate-way that relays packets between two points. With most application gateways, additional packet-filter machines are required to control and screen traffic between the gateway and the networks. A typical configuration includes two routers. With a bastion host that serves as the application gateway sitting between them. A drawback to application and circuit gateways is that they slow network performance. This is because each packet must be copied and processed at least twice by all the communication layers. Packet-filter gateways, which act as routers between two nets, are less secure than application gateways but more efficient. They are transparent to many protocols and applications, and they require no changes in client applications, no specific application management or installation, and no extra hardware. Using a single, unified packet-filter engine, all net traffic is processed and then for- warded or blocked from a single point of control. However, most packet filters are state- less, understand only low-level protocols, and are difficult to configure and verity. In addition, they lack audit mechanisms. Some packet filters are implemented inside routers, limiting computing power and filtering capabilities. Others are implemented as s9ftware packages that filter the packets in application-layer processes, an inefficient approach that requires multiple data copies, expensive delays and context switches and delivers lower throughput. So what’s a network administrator to do Some vendors are developing firewalls that overcome many of these problems and combine the advantages of application gateways and packet filtering. These efficient, protocol-independent, secure firewall engines are capable of application-level security, user authentication, unified support, and handling of all protocols, auditing and altering. They are transparent to users and to system setup, and include a GUI for simple and flexible system management and configuration. In choosing a firewall product, what is implied as the main concern of the author
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2003年7月5日，A纺织厂(以下简称“A厂”)与B棉麻公司(以下简称“B公司”)签订了一份买卖合同。该合同约定：B公司向A厂供应50吨一级皮棉，总价款为人民币130万元；在合同签订之后30日内，由A厂先期以银行承兑汇票的方式预付人民币30万元货款；B公司在同年10月上旬一次向A厂交货；A厂收到货物并验收合格后30日内一次向B公司付清余款；违约金为货款总值的5％，计6．5万元。与此同时，为了保证该买卖合同的履行，B公司要求A厂的控股投资公司即c纺织控股(集团)公司(以下简称“c公司”)就A厂依约履行付款义务提供担保，A厂表示由c公司提供担保较为困难，但可以找C公司在B公司所在城市的分公司提供担保，B公司表示同意。于是，该分公司便与B公司签订了保证合同。该保证合同约定，该分公司保证A厂履行其与B公司签订的买卖合同约定的付款义务，如果A厂不履行义务，该分公司保证履行。据查，该分公司没有c公司的书面授权。2003年8月1日，A厂为履行先期预付货款的义务，向B公司开出一张人民币30万元见票后定期付款的银行承兑汇票。B公司收到该汇票后于同月8日向承兑行提示承兑，承兑行对该汇票审查之后，即于当日在汇票正面记载“承兑”字样，签署了承兑日期和签章，同时记载付款期限为同年11月28日。B公司为支付D建筑公司(以下称“D公司”)的工程费，于同月20日，将该汇票背书转让给了D公司。2003年10月上旬，B公司依照上述买卖合同的规定向A厂一次交付货物，并经A厂验收，同年11月上旬，A厂向B公司提出：B公司交付的货物不符质量要求，要求退货；B公司声称其货物不存在质量问题，不同意退货；并要求A厂严格履行买卖合同，按时向B公司支付货款。随后，A厂以B公司交付的货物不符质量要求为由，要求承兑行停止支付由其开出的人民币30万元的银行承兑汇票。D公司在该汇票到期日请求承兑行付款时，该行拒绝付款，A厂应拒绝向B公司支付货款。经调查证实：B公司交付A厂的货物不存在质量问题，A厂之所以要求退货，主要是因其生产的产品不适应市场的需要，积压过多，销售发生严重困难，因此决定停止生产经营，以便择机转产。因A厂未按时付款的行为，B公司遭受经济损失10万元。要求：依据上述事实及有关规定，回答下列问题：(1)A厂是否存在违约行为并说明理由。(2)B公司可否依据保证合同，要求C公司的分公司承担违约责任及赔偿责任为什么(3)承兑行可否拒绝支付D公司提示的银行承汇票为什么(4)D公司在其提示的汇票遭拒绝付款后，可以向哪些当事人行使追索权(5)因B公司遭受的经济损失高于合同约定的违约金数额，B公司是否可以要求增加违约金数额为什么
境内机构原则上只能开立一个经常项目外汇账户，在同一银行开立相同性质、不同币种的经常项目外汇账户的，需另行提出申清由外汇管理部门核准。( )
外资企业清算结束前，外国投资者不得将该企业的资金汇出或者携带出中国境外，但可自行处理企业财产。( )
In the past few decades, remarkable findings have been made in ethology, the study of animal social behavior. Earlier scientists had (21) that nonhuman social life was almost totally instinctive or fixed by genetics. Much more careful observation has shown that (22) variation occurs among the social ties of most species, showing that [earning is a part of social life. That is, the (23) are not solely fixed by the genes. (24) , the learning that occurs is often at an early age in a process that is called imprinting. Imprinting is clearly (25) instinctive, but it is not quite like the learning of humans, it is something in between the two. An illustration best (26) the nature of imprinting. Once, biologists thought that ducklings followed the mother duck because of instincts. Now we know that. shortly (27) they hatch, ducklings fix (28) any object about the size of a duck and will henceforth follow it. So ducklings may follow a basketball or a briefcase if these are (29) for the mother duck at the time when imprinting occurs. Thus, social ties can be considerably (30) , even ones that have a considerable base (31) by genetics. Even among the social insects something like imprinting (32) influence social behavior. For example, biologists once thought bees communicated with others purely (33) instinct. But, in examining a "dance" that bees do to indicate the distance and direction of a pollen source, observers found that bees raised in isolation could not communicate effectively. At a higher level, the genetic base seems to be much more for an all-purpose learning rather than the more specific responses of imprinting. Chimpanzees, for instance, generally (34) very good mother but Jane Goodall reports that some chimps carry the infant. upside down or (35) fail to nurture the young.
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