Tax Software Hosting Risk Guide

The Cybersecurity Risk of Running ProSeries Desktop on a Local Network

Software: ProSeries Professional / Basic | Vendor: Intuit

Key takeaway

In a ProSeries desktop / network setup, every workstation that can reach the shared ProSeries data folder is part of the attack surface for the firm's entire return database, even when there are only two or three PCs in the office.

Who this applies to

Tax preparation firms, CPA firms, EAs, bookkeepers, EROs, and accounting offices that run ProSeries Professional / Basic on local PCs, mapped network drives, peer-to-peer shares, or an in-office file server.

ProSeries Professional / Basic is commonly used by tax professionals, and many firms run it as a desktop or local-network install because it is familiar, fast, and convenient. The tradeoff is that local convenience can create serious cybersecurity exposure when sensitive taxpayer data lives on office PCs, shared drives, mapped network paths, or an in-office file server.

What ProSeries Professional / Basic is

ProSeries Professional and ProSeries Basic, from Intuit, are widely used by independent preparers, small CPA firms, and high-volume 1040 practices. Intuit also offers ProConnect Tax Online and a hosted ProSeries option, but this article focuses specifically on firms running ProSeries Professional or Basic in a desktop / LAN-shared configuration where the application and return data live in the office.

How local ProSeries Professional / Basic setups usually work

A typical ProSeries network install places the application on each workstation and points everyone to a shared "ProSeries" data folder on a host PC or small server, usually via a mapped drive. Multiple preparers open returns from the same dataset over the LAN. Many small offices also run ProSeries on a single workstation that doubles as a "host" for one or two other PCs. Remote staff frequently connect through RDP or third-party remote tools, and backups are commonly handled by an external drive in the same office.

Quick definitions

Mapped drive — a Windows drive letter (like T:\ or Z:\) that points to a shared folder on another computer or server.
Local server / file server — a computer in the office that hosts shared files for other workstations.
Hosted server — a server in a controlled hosting environment (cloud or properly hardened internal) that users reach through controlled remote sessions.
MFA — multi-factor authentication; requires a second factor (app code, hardware key) in addition to a password.
WISP — Written Information Security Plan, expected of tax professionals under IRS Publication 4557 and FTC Safeguards Rule expectations.
Ransomware — malware that encrypts files and demands payment for a decryption key.

Why taxpayer data inside ProSeries Professional / Basic is so valuable

Return data inside professional tax software typically includes:

Names, addresses, and dates of birth
Social Security numbers and dependent information
Employer information and W-2, 1099, and K-1 details
Bank account and routing numbers used for refunds and payments
Prior-year return data and carryforwards
Tax credits, deductions, and filing status
Identity verification information
E-file submission data

That combination is exactly what attackers need for identity theft, refund fraud, business email compromise, extortion, and ransomware. It is a major reason tax offices are repeatedly targeted, particularly during filing season.

Risk summary

Local setup element	Why it creates risk	Better hosted-server control
Shared / mapped tax data folder	Malware on one workstation may reach all shared files	Keep tax data inside a controlled hosted session
Shared Windows credentials	Hard to prove individual accountability	Require unique user accounts with MFA
Local workstation storage	Data may remain on laptops and desktops	Centralize data on a secured, segmented server
Local backups	Backups may be reachable by ransomware	Use protected, segmented, monitored backups
Uncontrolled remote access	Attackers may abuse exposed RDP / remote tools	Use MFA-protected remote sessions only

The inherent problem with local network sharing

When ProSeries Professional / Basic data is shared over the office LAN, the security of the tax database effectively depends on the weakest workstation, weakest password, weakest Windows account, weakest remote access tool, weakest backup process, and weakest shared-folder permission in the office. Common risks include:

Compromised Windows logins and phishing attacks on staff
Malware on a single workstation that reaches all shared data
Ransomware encrypting mapped drives and reachable backups
Weak, reused, or shared passwords; no individual MFA on app access
Local admin rights granted too broadly
Exposed RDP or poorly secured third-party remote access tools
Unencrypted or co-located backups
Old workstations and missing patches during busy season
Inconsistent endpoint protection across the office
Over-permissive file shares with no centralized audit trail
No clear evidence of access controls or written security plan

Realistic attack scenarios

A small office uses one workstation as both reception PC and ProSeries host; a phishing click on that PC encrypts the entire data folder.
A preparer reuses a personal password that was breached; an attacker logs into a remote tool and accesses live returns.
A retired seasonal preparer's account is never disabled and is later abused to access prior-year client files.
Local backups on a USB drive plugged into the host PC are encrypted in the same incident as the live ProSeries data.
An exposed RDP port is brute-forced and used as the initial access path into the office network.

Why "we have antivirus" is not enough

Antivirus, endpoint protection, firewall appliances, spam filtering, and backups are useful — but they are not the same thing as a secure architecture. A ProSeries Professional / Basic office can still be exposed if a user is phished, a workstation is compromised, a mapped drive is reachable, a backup share lives on the same network, an attacker gains local admin rights, users share credentials, the tax app does not require individual MFA on every access, or the firm cannot prove who accessed which client file and when.

IRS, WISP, and the compliance angle

Tax professionals are expected to protect taxpayer data and to maintain a Written Information Security Plan (WISP). IRS Publication 4557 and the FTC Safeguards Rule frame this expectation in general terms: a firm needs more than good intentions. It needs documented controls, access management, incident response planning, employee training, backup and recovery planning, and security monitoring. This article is not legal advice — it describes architectural patterns that are easier or harder to defend during a review.

Why hackers target tax offices

Small and mid-sized tax firms are attractive targets because they:

Hold uniquely valuable identity and financial data
Often do not have full-time IT or security staff
Frequently rely on older local-network software workflows
Use seasonal preparers and rush operations during tax season
Sometimes delay patches and upgrades until "after April"
Commonly use multiple remote access tools
Allow a single compromised workstation to expose all shared tax data

A more defensible architecture: hosted server model

For ProSeries Professional and Basic, a more defensible setup runs the application inside a controlled hosted-server environment with per-user MFA-protected accounts, segmented backups, and no raw share exposure to ordinary office workstations or personal devices.

In a properly designed hosted-server model: ProSeries Professional / Basic runs on a controlled server, users access it through secure remote sessions, each user has an individual account, MFA is required, local desktops do not directly store or freely browse the tax database, access is logged, backups are centralized and segmented, permissions are enforced, security updates are managed centrally, and the environment is segmented from the rest of the office network. That is materially easier to document for WISP and compliance purposes than a peer-to-peer or mapped-drive LAN.

Important nuance

A "hosted server" can be either a reputable remote tax software hosting provider or a properly secured local server environment that is designed to behave like a hosted system — users authenticate individually with MFA and access the tax software through controlled sessions, instead of opening raw shared data from ordinary office desktops. The architecture matters more than the address.

Schedule a ProSeries Professional / Basic security review

If your firm runs ProSeries Professional / Basic from local desktops, mapped drives, peer-to-peer shares, or an office file server, EasyWISP can help you understand the risk, document your WISP, and plan a safer hosted-server model with individual access controls and MFA.

Schedule a Tax Software Security Review See How EasyWISP Helps Tax Firms

Frequently asked questions

ProSeries works on small peer-to-peer networks, but those setups are some of the hardest to defend: a single compromised PC typically has direct access to all shared ProSeries data, with limited logging and no real segmentation.

Yes. In a desktop install, return data including SSNs, dependents, W-2 / 1099 details, and refund deposit information lives on the workstation or shared folder where ProSeries data is kept.

Yes. ProSeries client data files live on a Windows file system and can be encrypted by ransomware running under an account with write access.

A properly run hosted ProSeries environment with individual MFA-protected accounts, centralized controls, and segmented backups is significantly easier to defend than a mapped-drive or peer-to-peer LAN setup.

Exposed RDP is a frequent initial access path for attackers. If used, it should always be behind MFA and ideally replaced by a controlled hosted-session model.

For most small firms, yes — the move dramatically improves the defensibility of the firm's WISP and reduces the impact of a single compromised workstation.

EasyWISP helps small ProSeries practices document their WISP, evaluate their existing setup, and plan a safer hosted-server architecture suited to their size.

Conclusion

ProSeries Professional / Basic is not automatically unsafe, and many firms have used it for years. The issue is that the local-network architecture gives attackers too many paths to taxpayer data when a single workstation, password, remote access tool, or mapped drive is compromised. For firms handling sensitive taxpayer information, the more defensible model is to move ProSeries Professional / Basic access into a controlled hosted-server environment with MFA, centralized backups, logging, segmentation, and documented WISP controls.