The Oak Brook data center houses critical corporate information and Web sites for about 70 Fortune 500 companies and smaller organizations. Those 70 companies account for about 70 percent of the space sold. The center is about 86,000 square feet. It just completed an addition of about 9,000 square feet. A second phase has started to add another 13,000 square feet and could be completed later this year.

More space could be added in the future, said company spokesman Brian Lustig.

For security reasons, Latisys declined to name the companies that use the data center. After all, it aims to keep the information and Web sites safe from hackers and other problems, said Lustig.

"I can tell you that the Latisys Oak Brook data center customer base is made up of large, recognizable locally headquartered enterprises as well as large financial services and trading firms," he said.

Data centers are playing a critical role in securing corporate information and Internet-related activities, including Web sites. It's also a growing industry, as proof of the major expansion in Oak Brook. As a result of this growth, Latisys plans to expand its Oak Brook workforce.

Latisys started the year with 14 and now has 28 employees. The company plans to add 33 percent to the staff in the next six months, bringing the workforce up to 37 by spring, Lustig said.