The H Security reports the Apache SpamAssassin spam filter was hit by a Y2K-like bug on New Year:
The Apache SpamAssassin spam filter has been shipping with a rule which defined any year past 2009 as "grossly in the future" and adding 3.2 to the email's spam score. The default threshold for spam is 5.0, so the error makes it much more likely that legitimate mail will be falsely marked as spam.
The problem was noted by Mike Cardwell, a UK based developer, who brought up the issue on the spam filter's mailing list. The problem had been reported in 2008 and fixed in the SpamAssassin repositories, but the rules were not backported to 3.2 for users until new years day when the omitted update was noticed.