Time and billing spreadsheets and AI data leakage: what a month-end WIP sheet gives away in ChatGPT or Claude.

Billing is the part of a law firm nobody enjoys, so it is where staff first reach for ChatGPT or Claude: tidy these narrations, spot the entries to write down, check the total. A work-in-progress sheet holds every matter, every fee earner, every narration and the notes beside them, and the narrations are written in the candid shorthand of people who expect only the partner to read them. This page marks every cell in a month-end billing sheet that rule 9, privilege and the new anti-money laundering rules bear on, and shows how the same sheet is cleaned up on Ermos inside the firm.

The time and billing spreadsheet

Exported from the practice management system at month end and reviewed by the partner before bills are issued.

An invented spreadsheet. Matter codes and amounts are invented and the entries use the cast of the other law firm pages. Hover or tap any highlighted item for the analysis; the full list is below.

What leaves the firm

1. 1
   Matter codes and client names

   Each code carries the client and the other side. A list of matters is a list of who has instructed the firm and against whom, which is confidential to each client under rule 9. Rule 9 confidentiality guide.

2. 2
   A candid narration

   A client’s state of mind, a change in medication, a job interview and the advice given, written as time entries. Privileged advice and health information in a billing line. Legal privilege guide.

3. 3
   A deal under NDA in a narration

   A named counterparty and a negotiating fallback, in a column the firm treats as routine. The deal is under a non-disclosure agreement the client signed. Rule 9 confidentiality guide.

4. 4
   Hours, rates and fee earners

   Who works on what, at what rate. Rates are disclosed to each client, but the full table is the firm’s own information.

5. 5
   A disbursement line

   A courier charge with no party or matter in the text.

6. 6
   Identity checks and customer due diligence

   A record that identity was verified and customer due diligence recorded before a property transaction. AUSTRAC lists assisting with the sale, purchase or transfer of real estate among the professional designated services regulated from 1 July 2026, and says the AML/CTF records are usually kept for seven years. Identity documents are personal information, and the entry sits in the billing system. Privacy Act guide.

7. 7
   Notes about write-downs and the NDA

   Partner-level notes on a client who is stretched and a reminder to narrate generically. Information about the client’s finances, and the firm’s own handling of an NDA. Rule 9 confidentiality guide.

8. 8
   An estate narration

   A named executor and a sibling’s threatened claim. Privileged assessment of a family dispute, in a time entry. Legal privilege guide.

9. 9
   The total and its formula

   A sum over a range and the figure it produces. It names no client.

10. 10
    A settlement narration

    The balance moving at settlement and the lender. The second fact a payment redirection fraud needs, in a column nobody thinks of as sensitive. Rule 9 confidentiality guide.

What happens in Frontier Models (ChatGPT, Claude)

• The whole document is transmitted to the provider’s servers. On personal plans the user cannot choose where it is stored or processed, and for the major providers that has generally meant outside Australia, under that country’s legal process. Some business plans offer storage in Australia, but the provider still receives the content.
• On consumer tiers, prompts can be retained and used to train future models.
• The provider’s staff and systems can reach the content under the provider’s own policies.
• Once sent, the firm no longer controls it. Retention and deletion happen on the provider’s terms.

The same document on Ermos

Part of AI data leakage in law firms.

Common questions