Law firms and data leakage: protecting client confidentiality

For a law firm, a data leak is not just a security incident: it is a potential breach of legal professional privilege, which engages the lawyer’s liability and the client’s trust. Most of these leaks do not come from a sophisticated attack, but from the firm’s ordinary actions: a misaddressed email, an exhibit dropped on a personal file share, a working draft sent from a phone. Preventing them means knowing these egress paths and checking, through concrete tests, that your controls actually close them.

Why a law firm is a target apart

A firm concentrates on a small number of workstations information that many companies spread across entire systems: merger projects, litigation strategies, medical records in a personal injury case, wealth data, confidential exchanges with an executive. A single case file can be of considerable value to a competitor or an attacker.

Legal professional privilege covers, in principle, legal advice, correspondence and the documents in the file. A leak is therefore not measured only in the number of records exposed, as in a standard processing register. A single internal memo can be enough to cause serious harm. That is what makes the “we will see at the next audit” approach so risky in this profession.

Another particularity: the organisation. Highly autonomous partners, mobile associates, assistants who handle the sending, constant exchanges with fellow lawyers, experts and clients who impose their own tools. The IT department, often outsourced or small, has to protect a scope it only partly controls.

The most common leakage paths

Email, the first channel

Email remains the central working tool. The risks are well known but rarely checked:

• The wrong recipient through autocomplete, which sends pleadings to opposing counsel instead of the client.
• Forwarding to a personal mailbox to “work on it this weekend”.
• Large attachments replaced by a sharing link open to “anyone with the link”.
• Metadata and comments left in a Word document sent to the opposing party.

If you have deployed outbound email rules, the question is not whether they exist, but whether they trigger. Our article on how to test your email DLP rules details this check.

File sharing and the tools imposed by clients

Data rooms, sharing platforms, the client’s collaborative workspaces, personal cloud to get around a size limit: each case creates new paths. The associate in a hurry has no bad intention. They are simply looking for the fastest way to send 400 pages of exhibits. These everyday leaks are covered more broadly in our article on personal cloud and collaboration tools.

Laptops on the move and peripherals

A USB stick handed to an expert, printing at home, a case folder synchronised to a personal computer. The lawyer’s workstation is often the least controlled exit point of the firm.

Generative AI

Summarising a ruling, rewording a clause, translating an exhibit: the temptation to paste an excerpt of a case file into a public assistant is strong. It is an egress channel in its own right, and must be treated as such.

What a written policy cannot guarantee

Many firms have an IT charter, annual awareness training and a DLP tool built into their office suite. That is necessary. It is not evidence.

A rule that detects internal case numbers will be useless if those numbers change format. An exception created for a partner two years ago may still cover their entire department. These gaps between configuration and reality are typically those described in our analysis of DLP false negatives: they fail silently, without an alert.

Tests suited to the reality of a law firm

Testing does not mean letting real client files out. The principle is to use synthetic data that looks like the firm’s documents (fake pleadings, fake contracts, fictitious case numbers in the right format) and to send it along the real egress paths. The general framework of this approach is presented in our page on data exfiltration testing.

Example of a concrete scenario

An associate prepares a fake strategy memo marked “Confidential, legally privileged”, containing a fictitious client name and a matter number in the internal format. The test then checks, channel by channel:

1. Is sending it as an attachment to an external personal address blocked, flagged or merely logged?
2. Is dropping the file on a personal storage service from the browser detected?
3. Is copying to removable media prevented on a laptop outside the firm’s network?
4. Does pasting the content into a public AI assistant trigger a control?
5. Who receives the alert, and how long before someone handles it?

Each answer is an observable fact. That is what distinguishes active testing from a compliance questionnaire.

Prioritisation table by channel

Scroll the table →

The insider threat, without presuming bad intent

The departure of an associate or a partner to a competing firm is a sensitive moment. Testing this scenario does not mean suspecting the teams. It is about checking that an unusual volume of files downloaded the day before a departure would be seen. The subject is developed in our article on the insider threat.

What the partner in charge or the IT director should check

• Identify the three or four most sensitive document types and how they are marked.
• List the egress channels actually in use, including those imposed by clients.
• Check that DLP rules are in blocking mode where justified, not just in audit mode.
• Inventory the exceptions granted and their date.
• Replay scenarios with synthetic data, then again after every change of tool.
• Turn every finding into a prioritised corrective action, with an owner.

Frequently asked questions