I too had to log in when I came back yesterday after seeing a notice about the software upgrade -- just assumed it was a cookie-reset thing related to the upgrade.
But I haven't seen anything about a security token, missing or otherwise... I feel a bit left out.
"Once the writer in every individual comes to life (and that time is not far off), we are in for an age of universal deafness and lack of understanding."
(Milan Kundera, Book of Laughter and Forgetting, 1980)