: Sequential or non-existent ZIP codes are a major red flag for fraud. For example, investigative reports on Reddit found that H-1B visa application fraud was uncovered when multiple companies used sequential, non-existent ZIP codes (e.g., 68000 through 68009 ) in their filings. Summary Table: Real vs. Frequently Used Fake ZIPs Primary Known Use 90210 Real Beverly Hills, CA (often used by non-residents) 12345 Real

: According to Transportation Insight , the highest valid U.S. ZIP code is 99950 (Ketchikan, Alaska). Despite this, many databases are filled with 99999 entries used as catch-all placeholders.

: Researchers noted on LinkedIn that attackers can host phishing pages on a .ZIP domain that perfectly emulates software like WinRAR.

: When users enter codes like 11111 , it violates business constraints and creates outliers in statistical models. Six Sigma methodologies are often employed to clean this "dirty data."