Mixed credit files, explained

Not every wrong item on your credit report got there through fraud. A "mixed file" is a bureau's own automated matching system doing exactly what it was built to do — and getting it wrong: merging your credit history with a stranger's, or a relative's, because enough identifying details lined up. It's a different problem from identity theft, it happens more than most people realize, and it doesn't always get fixed on the first dispute.

How two people's files become one

Equifax, Experian, and TransUnion each build your file automatically, matching incoming account data to an existing consumer record using an algorithm — not a person reviewing each entry. Documented industry practice, described in litigation and in the National Consumer Law Center's own reporting on the issue, has bureaus treating a match of as few as seven of the nine digits of a Social Security number, combined with a matching name and state, as sufficient to fold new data into an existing file. That threshold is loose enough that a parent and adult child with the same name (a "Jr." and "Sr."), two unrelated people with a common name in the same city, or simply a data-entry transposition of two digits can produce a false match — at which point someone else's credit card, loan, or collection account starts appearing on your report, and yours might start appearing on theirs.

Not the same thing as identity theft

It's worth being precise about the distinction, because the fix is different. Identity theft is someone deliberately using your information to open an account fraudulently; a mixed file is nobody's account being stolen — it's a bureau's own matching logic incorrectly attaching a real person's real, legitimately-opened account to your file instead of theirs. The rapid, four-business-day block procedure covered in blocking fraudulent information from your credit report exists specifically for fraud, and generally requires an identity theft report; a mixed file is disputed under the ordinary FCRA reinvestigation process instead, because there's no fraud to report — just bad data that needs to be separated back out.

How common this actually is

The FTC's congressionally mandated study of credit report accuracy under Section 319 of the Fair and Accurate Credit Transactions Act — the most rigorous government research on this question, based on a sample of several thousand consumers who each reviewed their own three reports — found that one in five had an error on at least one report that a bureau corrected after a dispute, and that five percent had an error serious enough that it could have led to paying more for a loan or insurance. That study didn't break its findings down specifically by how many errors were mixed-file cases versus other kinds of inaccuracies, so it isn't evidence for a specific mixed-file percentage on its own — but it does establish, from the government's own numbers rather than an industry or advocacy estimate, that materially wrong information persisting until disputed is a real, non-trivial share of credit reports, not a rare edge case.

A live example, not a hypothetical: on 7 January 2025, the CFPB sued Experian (CFPB v. Experian Information Solutions, Inc., No. 8:25-cv-00024, C.D. Cal.), alleging the company ran "sham" reinvestigations of consumer disputes — deferring uncritically to the furnisher's side of the story, failing to pass along documentation consumers submitted, and in some cases letting previously deleted inaccurate information reappear on a file. The court denied Experian's motion to dismiss in October 2025 and the case remains pending, with Experian having filed its answer in November 2025 — a live, unresolved case rather than a settled finding of wrongdoing, but a concrete, currently active example of the exact failure mode a mixed-file dispute can run into: a computer-matched error met with an equally automated "verified as accurate" response.

Why the first dispute sometimes doesn't fix it

An ordinary FCRA dispute (15 U.S.C. § 1681i) triggers an automated reinvestigation in which the bureau sends the disputed item's furnisher a short, coded summary of your dispute and asks it to confirm or correct it — a process largely run through an industry-shared system, not a human reading your actual letter. A generic dispute that just says "this account isn't mine" can get matched against the furnisher's own records, which show a real account with a real matching name and partial SSN, and come back "verified" — because from the furnisher's side, nothing looks wrong. A mixed-file dispute tends to need more specificity to break that cycle: stating plainly that the account belongs to a different, identifiable person (not simply "this is inaccurate"), and providing something the automated match can't already see — a copy of your Social Security card, a full nine-digit SSN comparison if you have reason to believe the confusion is digit-based, or documentation that you've never lived at an address tied to the disputed account.

What to actually do

Pull all three reports, not just one. A mixed file is often bureau-specific, since each one runs its own separate matching system — a mistaken merge at Experian doesn't mean the same error exists at Equifax or TransUnion, and one report can act as a comparison for what your own accurate history should look like.
Dispute in writing, specifically. Identify the exact account, state that it belongs to a different, real, identifiable person rather than describing it as merely wrong, and include a copy of your driver's license and Social Security card if you're comfortable sending them (mail a copy, not the original).
Use the furnisher route too. See furnishers and your FCRA dispute rights for the separate right to dispute directly with the company that reported the account, alongside the bureau.
If the bureau "verifies" it anyway, escalate. A second written dispute that specifically references the first one and notes it wasn't genuinely investigated carries more legal weight than repeating the same generic online dispute form a second time. A complaint filed with the CFPB creates a paper trail a bureau has to formally respond to.

Related: a mixed file and a case of actual identity theft can look similar from the outside — see blocking fraudulent information from your credit report for the separate, faster process that applies when the account really was opened fraudulently in your name.