The Year 2010 problem (also known as the 2010 bug) refers to a number of software errors that occurred across various systems around the turn of the year 2009/2010.

Y2K10: When millions of debit cards failed due to a date programming bug

The most widely reported incident stemmed from a programming error in certain debit and credit cards that left more than 30 million cards temporarily unusable. Dutch company Gemalto took responsibility for the glitch. The issue was resolved by reconfiguring terminals to read the magnetic stripe instead of the EMV chip, which by that point had already been considered outdated. Several banks, including savings banks, agreed to reimburse customers for any related expenses—such as fees for international transfers made during vacations.

In Australia, ATMs belonging to the Bank of Queensland became inoperable due to an error that set the system date to 2016, causing customer cards to be falsely flagged as expired.

An issue with the SpamAssassin spam filter led to many emails sent after December 31, 2009, being wrongly classified as spam. Email providers GMX and 1&1 were among those affected. The root cause was an incorrect filtering rule.

Since January 1, 2010, text messages sent from smartphones running Microsoft’s Windows Mobile 6.1 and 6.5 have been displaying incorrect timestamps—listing the sending date as sometime in 2016.

Users of SAP’s ERP software also encountered problems: spool entries had their expiration dates calculated incorrectly due to a date-handling bug.

Symantec’s Endpoint Protection Manager, a corporate security platform, mistakenly flagged virus definition files dated in 2010 as outdated, preventing proper updates.

Apple’s Newton PDAs suffered from an integer overflow in their date calculations, causing alarm notifications scheduled after January 5, 2010, at 6:48:31 p.m. to enter an endless repeat loop.

Unlike the heavily publicized Y2K or “Millennium Bug,” which was largely resolved in advance of the year 2000, the Year 2010 problem arose unexpectedly and took time to correct. In hindsight, Y2K’s minimal real-world impact was likely thanks to extensive preparation in the lead-up to the 1999/2000 transition.

Year 2010 problem: Causes of the forgotten date bug

Some systems, especially those using EC cards, stored years using BCD (Binary-Coded Decimal), where each digit is represented by four bits. A two-digit year stored as X'10' (binary 0001 0000) could be misinterpreted as a full one-byte integer, leading to confusion between 10 and 16 in certain cases.

In other programs, the date format was hardcoded to expect years in the 200x range. As a result, data from the year 2010 was mishandled or rejected outright. Outside the realm of software, Y2K evolved into a pop-cultural symbol—fueling a nostalgic aesthetic trend in fashion and design, inspired by that turn-of-the-millennium digital era.

Year 2010 bug also discovered on computers

Initially, the 2010 bug was an annoyance mostly affecting around 30 million EC and credit card holders, many of whom were unable to access their accounts or make payments as of January 1, 2010. But the issue also impacted Microsoft systems. Some users of smartphones were surprised to find that messages sent since New Year’s Day were dated 2016. Devices running Windows Mobile versions 6.1 and 6.5 were particularly affected.

The problem stemmed from flawed internal date conversion routines—a classic case of sloppy date handling in code. Internally, the software operated using the hexadecimal system, converting to decimal format only at the final output stage. The two number systems are identical from 0 to 9 but diverge beyond that, which explains the misalignment. The following table would illustrate how hexadecimal values can lead to confusion if misinterpreted as decimal—but was omitted here for brevity.

Year 2010 problem in GMX spam filter

Since New Year’s Day, GMX’s spam filter began flagging an unusual number of emails as spam—apparently because they seemed to originate “from the future.”

Users of GMX should check their spam folders: the service’s filtering engine appears to be misinterpreting the year 2010, causing it to incorrectly reject valid emails. Headers often contain entries like:

X-GMX-Antispam: 5 (Score=6.300;BAD_ENC_HEADER,FH_DATE_PAST_20XX);

The key part here is FH_DATE_PAST_20XX—a rule designed to detect emails dated suspiciously far into the future. In this case, the filter seems to have mistaken legitimate messages as violating that condition. GMX isn’t alone; 1&1 was also impacted by the same issue. The bug was traced back to SpamAssassin, a widely used spam filter framework. The error has since been documented.

Anyone relying on server-side spam filtering should remain vigilant—your filter could still be running a version of SpamAssassin that suffers from the Year 2010 bug.