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network.

In this case, the attacker will look the system over for weaknesses. And possibly make many different kinds

of attempts, until he finds a crack to wiggle through. Or gives up. This is more difficult to defend against. The

attacker is armed and dangerous, so to speak, and is stalking his prey.

Again, this scenario is very unlikely for a typical home system. There just generally isn't any incentive to take

the time and effort when there are bigger fish to fry. For those who may be targets, the best defense here

includes many of things we've discussed. Vigilance is probably more important than ever. Good logging

practices and an IDS (Intrusion Detection System) should be in place. And subscribing to one or more

security related mailing lists like BUGTRAQ. And of course, reading those alerts daily, and taking the

appropriate actions, etc.

8.4.7. Denial of Service (DoS)

"DoS" is another type of "attack" in which the intention is to disrupt or overwhelm the targeted system or

network in such a way that it cannot function normally. DoS can take many forms. On the Internet, this often

means overwhelming the victim's bandwidth or TCP/IP stack, by sending floods of packets and thus

effectively disabling the connection. We are talking about many, many packets per second. Thousands in

some cases. Or perhaps, the objective is to crash a server.

This is much more likely to be targeted at organizations or high profile sites, than home users. And can be

quite challenging to stop depending on the technique. And it generally requires the co−operation of networks

between the source(s) and the target, so that the floods are stopped, or minimized, before they reach the

targeted destination. Once they hit the destination, there is no good way to completely ignore them.

"DDoS", Distributed Denial of Service, is where multiple sources are used to maximize the impact. Again,

not likely to be directly targeted at home users. These are "slaves" that are "owned" by a cracker, or script

kiddie, that are woken up and are targeted at the victim. There may be many computers involved in the

attack.

If you are home user, and with a dynamic IP address, you might find disconnecting, then re−connecting to get

a new IP, an effective way out if you are the target. Maybe.

8.4.8. Brute Force

"Brute force" attacks are where the attacker makes repetitive attempts at the same perceived weakness(es).

Like a battering ram. A classic example would be where someone tries to access a telnet server simply by

continually throwing passwords at it, hoping that one will eventually work. Or maybe crash the server. This

doesn't require much imagination, and is not a commonly used tactic against home systems.

By the way, this is one good argument against allowing remote root logins. The root account exists on all

systems. It is probably the only one that this is true of. You'd like to make a potential attacker guess both the

password!

Security Quick−Start HOWTO for Red Hat Linux

8.4.7. Denial of Service (DoS) 59

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Red Hat NETSCAPE MANAGEMENT SYSTEM 6.2 - COMMAND-LINE Guida di Installazione Pagina 62