But that may not necessarily be the case, according to a new report from researchers at the University of Maryland (UM).
In UM's test environment, port scans preceded attacks in only 5 percent of cases. The report also found that more than half of all attacks are not actually predicated by any type of scan. "Hackers don't necessarily look before they leap," the study concludes.
"I was surprised that the percentage was that low," Michel Cukier, a UM assistant professor and one of the report's authors, said.
Cukier noted that the results may have been influenced by some the decisions made in UM's testbed.
"It would be interesting to repeat the experiment on other locations with other choices," Cukier told internetnews.com.
Though port scanning was not a predictor for attacks, vulnerability scans do in fact lead to attacks in a significant percentage of cases. The UM report defines vulnerability scanning as a scan "used to fingerprint the presence or absence of an exploitable vulnerability."