Are the sql parameterised query completely secure ?

Question

I have been coding on highly sensitive databases for sometime now , and has been using parameterised sql query like,

sqlcommand cmd = new sqlcommand("insert into register values(@name,@phone_no"),connection);

cmd.parameters.add('@name',name);

cmd.parameters.add('@phone_no',phone_no);

does these things could be trespassed , or the malicious instruments are completely nullified 

And how to secure data tampering ?