A report made public Wednesday on an internal investigation examining a week of computer use found more than more than 1 million log entries in which 7,700 employees visited game and auction sites.
More than 4,700 log entries were to sexually explicit and gambling Web sites.
The findings are "egregious" and "alarming," the department's inspector general, Earl Devaney, wrote in the report.
"Computer users at the department have continued to access sexually explicit and gambling Web sites due to the lack of consistency in department controls over Internet use," he wrote.
Devaney titled his report, "Excessive Indulgences." Its cover illustration is a photo montage of the types of Web sites employees have visited. One picture includes a shot of a woman's bare stomach.
Department officials say they are taking action to cut back on abuses by the agency's almost 80,000 employees with Internet access.
Devaney said in his report that he wanted to test the effectiveness of the department's rules on Internet usage. He looked primarily for visits to sexually explicit, gambling, gaming and auction sites because they are time-consuming and obviously not work-related, he said.
The investigation also found:
A number of computers accessed sexually explicit Web sites for 30 minutes to an hour.
One computer had 2,369 log entries at two game sites for about 12 hours.
At least one computer accessed an Internet auction for almost eight hours.
Despite the findings, Devaney noted that since 1999, the department has taken just 177 disciplinary actions, 112 of which were for accessing pornographic or sexually explicit Web sites.
"Without strong and effective controls, we believe that this activity will continue and possibly increase," Devaney wrote.
In response, department officials issued a memo to all employees on Sept. 27 reminding them that some of the activities Devaney found "have significant legal and administrative consequences" and that violators could be fired or turned over to the police.
The department is working on blocking inappropriate Internet sites, the memo said. But it reminded employees that "just because an inappropriate site is not blocked does not mean that it is authorized for access."