"All it takes in Los Angeles County to be declared the father of a child — and therefore on the hook for any and all back child support, with interest — is for a mother to provide your name, the Department of Child Support Services to send you a summons choked in legalese, and for you to fail to return it within 30 days.
Such "default judgments"— which amount to 45% of all paternity-establishments in the state of California in 2005 (down from an appalling 68% five years previous) — are notoriously hard to undo once the wheels of justice are set in motion (greased by states' financial incentives from the federal government to establish as many paternities as possible).
It happened recently to a 19-year-old Palmdale kid (said to be the father of four). It's happened to untold numbers of gay men, and women with manly first names. It happened to a good friend of mine, whose never-used Christian name (Anthony Pierce) was uttered by a woman he'd never met in Northern California, thus putting him on the hook for a 10-year-old."