From the news release:

The Census Bureau today reported that a file containing limited respondent information on 302 households, commingled with fictitious test records, was improperly posted on one of the agency’s externally accessible servers in violation of strict agency policies regarding the protection of respondent information. The file was immediately removed. No Social Security numbers were contained in the files and the Census Bureau has no evidence that any respondent data were misused.

“As soon as we learned of the improper posting, we moved quickly to fix the problem. We immediately shut down the site and began an investigation,” said Census Director Charles Louis Kincannon.