Stafford Loans are just one of the loan types provided by the Department of Education. Other programs include Perkins Loans, PLUS Loans to parents and Pell Grants, which are not actually loans because they are not repaid. None of these loan programs requires collateral and are therefore all unsecured loan programs.
Since no federal student loans are secured with collateral, the borrower will not place any asset at risk in order to obtain the loan. If the student defaults on a Stafford Loan, the federal government can attempt to recover through collection agencies and wage garnishment, but it cannot attempt to reclaim an asset from the borrower.
The cause for confusion over whether Stafford Loan programs are secured likely comes from the fact they are "subsidized" or "unsubsidized." This means something completely different altogether. A subsidized borrower does not make payments while he is in school, and no interest is charged during that period of time. You must qualify based on income for this program. An unsubsidized borrower may defer loans until after graduation, but he will be assessed interest during that time period.