int payee Lst Id = Parameter('payeelstid'); account From = Acct Number By Index(payee Lst Id); Not only is this easier to render in HTML, it makes validation and business rule validation trivial. To provide defense in depth and to prevent attack payloads from trust boundaries, such as backend hosts, which are probably incapable of handling arbitrary input data, business rule validation is to be performed (preferably in workflow or command patterns), even if it is known that the back end code performs business rule validation.This is not to say that the entire set of business rules need be applied - it means that the fundamentals are performed to prevent unnecessary round trips to the backend and to prevent the backend from receiving most tampered data.Otherwise, you are allowing attackers to repeatedly attack your application until they find a vulnerability that you haven't protected against.
or Java Script or similar, reject strings containing them.
Note that you should proceed to validate the resulting numbers as well.
As you see, this is not only beneficial for security, but it also allows you to accept and use a wider range of valid user input.
For example, if you use HTML entity encoding on user input before it is sent to a browser, it will prevent most XSS attacks.
However, simply preventing attacks is not enough - you must perform Intrusion Detection in your applications.
Say you want to set up a site where users can upload arbitrary files so they can share them or download them again from another location.