Internet service providers: the little man's firewall?
A large percentage of malicious traffic is focused on a small number of vulnerabilities and their associated ports. Blocking some of these ports will isolate infected machines and slow the spread of malicious, autonomous code such as worms. However, the vulnerable services used by these worms do have legitimate uses. If secured properly, they can be used without the risk of infection. In this paper, we focus on ISPs that provide Internet access to consumers. This paper assumes that a consumer is a home user or a small business without dedicated IT staff. This paper does not apply to backbone infrastructure providers or co-location providers.
In part of this paper, we argue for blocking ports commonly used for Microsoft File sharing and related services; specifically, ports 135, 137, 139, and 445. These ports and, in particular, Microsoft File Sharing, draw a lot of attention from malware authors.
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