Taking Your Software Further: IRS Compliance Tool Rebuilt in 48 Hours
How Deltum rebuilt a decade-old FATCA compliance application from an unfamiliar codebase, in 48 hours, before an IRS submission deadline that could not move.
48hrs
From Brief to Delivered
10yrs
Legacy Codebase Age
0
Days of Manual Workaround
100%
IRS Submission Compliance
The Problem
A South African tax and regulatory compliance firm had been using an internal Windows desktop application to prepare and package FATCA data for annual submission to the IRS. The tool had been built in 2016 and quietly updated in 2020, but nobody had needed to look at the codebase since.
Then Windows 11 arrived. The application, built on a decade-old .NET stack, was no longer compatible with the modern operating system. With the annual IRS submission window approaching, the team faced a hard deadline and a tool that no longer ran.
Hard Regulatory Deadline
FATCA submissions to the IRS run annually. Missing the window means non-compliance, carrying real financial penalties. The deadline could not be moved, negotiated, or extended.
The Manual Fallback Takes Days
Without the tool, the team faced a multi-day manual workaround to prepare and package the submission data. Beyond the time cost, manual processes introduce error risk in a zero-tolerance regulatory environment.
Deltum Had Never Seen the Code
There was no handover, no documentation, and no original developer to consult. Deltum was handed a broken application, a GitHub repository, and a deadline.
The Solution
Deltum took the existing codebase, understood it from scratch, and rebuilt the application in the latest Visual Studio, fully compatible with Windows 11, backwards compatible with Windows 10, and delivered in 48 hours.
Codebase Review: From Cold Start
With no briefing from an original developer, Deltum read and understood a decade-old .NET application handling encrypted FATCA package generation, certificate signing, and IRS-compliant ZIP file creation, all within hours of receiving the brief.
Rebuild in Modern Visual Studio
The application was rebuilt using the latest Visual Studio toolchain. Compatibility issues with Windows 11's updated security and runtime environments were identified and resolved. All helper libraries were updated or replaced.
Encryption & Certificate Handling
The signing certificate, encryption key, and IRS-standard payload packaging logic were validated and updated, maintaining full compliance with the IDES (International Data Exchange Service) specification.
Three Deliverables, One Build
The client received the project file for future changes, a portable executable for running the app without an IT installation request, and a compiled setup.exe for full workstation deployment, eliminating dependence on internal IT teams for every update.
The Result
IRS submission completed on time. No penalties, no manual workaround, no missed window.
Application runs natively on Windows 11 with full compatibility for ongoing OS updates.
Backwards compatible with Windows 10. No forced upgrade required across the team.
Portable executable means the team can run the tool without raising an IT installation request.
Client holds the project file. Minor future changes can be made independently without returning to a developer.
"A decade-old codebase, an unfamiliar stack, a live regulatory deadline. Delivered in 48 hours."
Key Takeaways
Legacy Code is a Business Risk
Software built on an old stack doesn't break gradually. It breaks suddenly, often at the worst possible moment. Proactive modernisation is cheaper than an emergency rebuild under deadline pressure.
Speed Matters in Compliance
Regulatory windows don't flex. When a compliance tool fails, the clock is already running. The ability to move fast on an unfamiliar codebase is the difference between a fine and a clean submission.
Own Your Software
The client left with the source code, a portable executable, and a setup installer. They are not dependent on any developer, including Deltum, to keep running.
Got Software That's Fallen Behind?
Whether it's a legacy tool that stopped working or a codebase that needs taking further. We can assess it, modernise it, and hand it back to you running.