Most network applications authenticate users with an accountname/password system. Systems using reusable passwords are susceptible to attacks based on the theft of the password. One-time password systems attempt to alleviate the problem of "sniffed" passwords by making the replay of a password useless. However, one-time password systems require the use of a generator that creates the one-time password. The added inconvenience (and in some cases cost) of the generator has limited the wide spread application of one-time password systems. OPA (One-time Password Algorithms) implements a system that allows users to protect their accounts with a one-time password that adds minimal additional complexity over a simple reusable password system. OPA does NOT offer the degree of security provided by most other one-time password systems but can provide additional security when compared to reusable passwords.