Are Checks Sent Through the Mail Vulnerable to Theft?

The New York Times tells the story of a 63-year-old retiree who wrote a check for several thousand dollaras to pay her taxes. But she discovered much later that her taxes were never paid because that check had been intercepted and then altered to be payable to someone else:
In some cases, thieves may pilfer one or more checks from local mailboxes. Adam Rust, director of financial services for the Consumer Federation of America, said thieves sometimes "fish" for checks at free-standing drop boxes