"In June 2013, VA’s former chief information officer held a chat forum on the platform, “giving the false impression that VA approved the use of Yammer.com,” IG officials said. In fact, VA officials have not approved use of Yammer for any department work, despite the large number of employees on the site."
Sounds more like it wasn't made clear what was or wasn't an okay internal communication tool, which points to a lack of training and IT management.