We must provide the ability of fault tolerance mechanism in the runtime system when doing INTERNET based computing. This is due to the reliability of the computer system and the INTERNET itself. Sometimes, after we migrate the tasks to sonther computer, we will not get the results due to the fail of the computer system, and sometimes, we will also face the fact that we can't get the results because of the network, even another computer have finished the computation correctly. A possible fault tolerance approach is to execute ``hot spare'' tasks on otherwise idle computer system. These tasks can be generated using the migration facilities. If a computer fails while running a task with a backup task, the backup can be plugged into the remaining parallel program and execution can continue. For full fault coverage, every task would be duplicated on a different processors. However, if idle computers are available, some measure of redundancy is available for very little incremental cost.