DES MOINES (AP) - The Iowa Department of Transportation has blocked the use of several online social networking sites from employee work computers because of security concerns.

The agency's spokeswoman Dena Gray-Fisher says there are vulnerabilities and the department isn't going to take the risk.

She says she's concerned about potential computer hackers.

The blocked sites for the department's 3,000 employees include Twitter, Facebook and MySpace.

There are similar rules at the University of Iowa and the University of Northern Iowa.