Weapons of mass deception

Automated sock puppets are now (likely) in use by the US military, using software developed to enable a single person to maintain multiple credible and untraceable online personae. I spoke about this technology back here. The Pentagon claims it is being used for "counter-propaganda" purposes, noting that it would be illegal for them to use it on US citizens. It is clear that the military are not the only ones using it. Is it illegal for major corporations to do so?