Yes, as well as utilities, banks, insurers, hospitals, etc, etc. Treating the SSN as a password is idiotic, to the point where I almost wish Anonymous or someone would publish every American's number so that we'd be forced to stop doing it.
http://www.sciencemag.org/news/2009/07/social-security-numbe...
The actual situation is quite a bit less dire than your quote.
What that linked article says is that for people born AFTER 1989, the first five digits could be guessed with 44% accuracy. (There's a very real sense that the "last 4 of your social" are less guessable than the first five, so it's no surprise that the last 4 is what is often used/misused.)
If you have those last 4 digits, and you can guess the first 5 digits with nearly 50% accuracy, then you have a very good chance on getting legitimate SSN's for mass numbers of people with a DB dump.
for($i = 0; $i < 1000000000; $i++) {
print str_pad($i, 9, '0', STR_PAD_LEFT) . "\n";
}