IRS Form 990, submitted annually by tax-exempt organizations, is a public document, unlike Form 1040 individual taxpayers file. 132,362 charitable organizations published 472,866 Social Security numbers, of which 171,005 were unique. 18 percent of all not-for-profit organizations or their tax preparers published at least one Social Security number on their public tax return. Some organizations reported no identifying information at all, some published scholarship recipient names and some published names, addresses, SSN numbers.”]
Source: https://www.cuinfosecurity.com/blogs/kindness-repaid-by-exposing-your-ssn-p-1240