Among the key findings: Weak passwords really do make hackers' jobs much easier. The study also found that improved selection of usernames and associated passwords can make a big difference in whether attackers get into someone's computer.

The study was led by Michel Cukier, an assistant professor of mechanical engineering and an affiliate of the university's Clark School Center for Risk and Reliability and Institute for Systems Research. His goal was to look at how hackers behave when they attack computer systems -- and what they do once they gain access.

Using software tools that help hackers guess usernames and passwords, the study logged the most common words hackers tried to use to log into the systems. Cukier and two graduate students found that most attacks were conducted by hackers using dictionary scripts, which run through lists of common usernames and passwords in attempts to break into a computer.

Some 825 of the attacks were ultimately successful and the hackers were able to log into the systems. The study was conducted between Nov. 14 and Dec. 8 at the school.

Cukier was not surprised by what he found. "Root" was the top guess by dictionary scripts in about 12.34% of the attempts, while "admin" was tried 1.63% of the time. The word "test" was tried as a username 1.12% of the time, while "guest" was tried 0.84% of the time, according to the experiment's logs.