[ This is bug affects only to people using the spamassassin spam filtering software ]
Fabian Arrotin reports about this spamassassin bug, which tags mails dated 2010 and later - as potential spam (increases its spam-score). This is not silly - many spammers use fictional (far past/future) dates, wishing their spam would stay in the top/bottom of the long list of mails.
This bug alone didn't cause false positives in my spam folder (only increased the score from 0.0 to 0.6), but in some configurations or situations it could happen.
The bug was discovered about two hours after the first appearance of 2010 (UTC), and got fixed* a few hours later.
I was surprised to discover the sa-update tool which is an integral part of the spamassassin package. It fetches the updated rule sets to /var/lib/spamassassin dir, which spamassassin is aware of by default. This directory's files override the shipped, old rules in /usr/share/spamassassin.
After this incident, I linked this file /usr/share/spamassassin/sa-update.cron to the /etc/cron.daily dir.
* The fix, by the way, is quite a patch - it makes sure the mail's date is not after 2020.. I smell a repeat of events 🙂