14,562 research outputs found
New Sequential Methods for Detecting Portscanners
In this paper, we propose new sequential methods for detecting port-scan
attackers which routinely perform random "portscans" of IP addresses to find
vulnerable servers to compromise. In addition to rigorously control the
probability of falsely implicating benign remote hosts as malicious, our method
performs significantly faster than other current solutions. Moreover, our
method guarantees that the maximum amount of observational time is bounded. In
contrast to the previous most effective method, Threshold Random Walk
Algorithm, which is explicit and analytical in nature, our proposed algorithm
involve parameters to be determined by numerical methods. We have developed
computational techniques such as iterative minimax optimization for quick
determination of the parameters of the new detection algorithm. A framework of
multi-valued decision for testing portscanners is also proposed.Comment: 11 pages, 5 figures, the mathematical theory of the detection
algorithm has been presented in SPIE conference
Methodological Issues in Multistage Genome-Wide Association Studies
Because of the high cost of commercial genotyping chip technologies, many
investigations have used a two-stage design for genome-wide association
studies, using part of the sample for an initial discovery of ``promising''
SNPs at a less stringent significance level and the remainder in a joint
analysis of just these SNPs using custom genotyping. Typical cost savings of
about 50% are possible with this design to obtain comparable levels of overall
type I error and power by using about half the sample for stage I and carrying
about 0.1% of SNPs forward to the second stage, the optimal design depending
primarily upon the ratio of costs per genotype for stages I and II. However,
with the rapidly declining costs of the commercial panels, the generally low
observed ORs of current studies, and many studies aiming to test multiple
hypotheses and multiple endpoints, many investigators are abandoning the
two-stage design in favor of simply genotyping all available subjects using a
standard high-density panel. Concern is sometimes raised about the absence of a
``replication'' panel in this approach, as required by some high-profile
journals, but it must be appreciated that the two-stage design is not a
discovery/replication design but simply a more efficient design for discovery
using a joint analysis of the data from both stages. Once a subset of
highly-significant associations has been discovered, a truly independent
``exact replication'' study is needed in a similar population of the same
promising SNPs using similar methods.Comment: Published in at http://dx.doi.org/10.1214/09-STS288 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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