Internet-based communication is now frequently subject to electronic vandalism. As the sophistication of measures intended to combat such vandalism grows, new forms of vandalism appear. For example, a worm known as W32.SQLExp.Worm, or more simply as the Slammer Worm, appeared in late January, 2003. The Slammer Worm inflicted damage upon its victims by sending 376-byte packets to UDP port 1434, which is the SQL Server Resolution Server Port, and in effect provided a Denial of Service attack. One highly damaging attribute of the Slammer Worm was its unprecedented rate of growth and propagation, reportedly doubling itself every 8.5 seconds.
Spam (unsolicited and unwanted e-mail) can pose serious Denial of Services (DOS) problems by consuming resources. Spam can also carry payloads such as Trojans (code that may attempt to acquire unauthorized access to files or engage in other malicious activity). The problem of automatically discarding spam traffic is difficult to solve satisfactorily because the traffic can be at a high rate and can be difficult to distinguish from legitimate-traffic.
Such extreme forms of vandalism exceed the capabilities of known defensive mechanisms, sometimes even turning the defensive mechanisms themselves into Pyrrhic exercises that are accompanied by so many unintended consequences as to make their benefits questionable. For example, to combat the Slammer Worm, all traffic that includes UDP port 1434 in a source or destination address may simply be blocked. Unfortunately, this disrupts any flow of legitimate traffic that happens to include the same identification. Perhaps more troublesome, any appearance of legitimate traffic for UDP 1434 may trigger defensive measures even in the absence of the Slammer Worm.
Instances of invoking defensive measures in the absence of an intended trigger may generally be called false positives. Conversely, failing to recognize an intended trigger, or allowing any substantial delay once a trigger is detected, may permit fact-acting agents of vandalism such as the Slammer Worm to inflict severe damage before being brought under control. Such instances of failing to invoke defensive measures in the presence of an intended trigger may generally be called false negatives.
To combat rapidly propagating agents of vandalism such as the Slammer Worm, or of distributing spam e-mail, there is a need for an improved method of applying measures that defend against malicious traffic, where the improved method has a low rate of false positives, so that legitimate traffic unrelated to vandalism is not blocked, and also has a low rate of false negatives, so that fast-acting agents of vandalism are not allowed to inflict significant damage before they are blocked.
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