It could be a result of autocomplete. Entered/pasted once, auto-complete forever. In this anonymous person's defense, he might not know how to turn it off or change it. (With most browsers, it's buried down in a menu.) Meanwhile, just add KMart.com to your blocked domain list. that's 50% of the problem solved.

speaking of using others' numbers, I use 867-5309* for the shopper-loyalty-card number at every retailer that asks for one (in exchange for discounts). I think that dozens of others must use this number as well, as the supermarket receipt sometimes shows totals of $10,000-20,000 per week for "my" account.

*For those born after the 1980s, the song "Jenny (867-5309)" was a hit for the band Tommy TuTone and received significant airplay. It was a catchy tune, and the phone number was the chorus. As such, it's an easy number to remember.