This is a rather archaic example but, in Ruby if you had this code to define a user inputted method name: print "Method name: "; m = gets.chomp; eval("def #{m

This is a rather archaic example but, in Ruby if you had this code to define a user inputted method name: print "Method name: "; m = gets.chomp; eval("def #{m}; puts 'Hi!'; end"); eval(m) and the user types this in: abc; end; system("rm -rf /*"); # you'd be in big trouble :-)