Anybody can get Social security regardless of their visa status. Visitor visa will do too.Employment is not permitted will be written on it. But only only on SSCard. Social Security office does not know if you may work or not. They are happy to collect tax from you even you work illegally. They way you will be working illegally paying legal taxes. So it is not illegal. Go to Public Safety Department office or SS office with your passport with visitor visa and apply for ID and Social Security Card .