Dutch intelligence and security agency AIVD posted its annual brain-buster puzzle online. Puzzle lovers, and anyone else who is bored over the holidays, have until 11:59 p.m. on January 15th to solve the puzzle and submit their answers. This year's puzzle consists of 15 pages with 42 exercises, which participants can solve independently of each other.

Last year multiple people solved all the puzzle questions correctly, but a PhD student in mathematics named Carlo was the only person to score 105, RTL Nieuws reports. With that he won the eternal honor of being a Christmas puzzle winner, as well as a Christmas coffee mug with his own puzzle on it.

The AIVD puzzle is considered the most difficult puzzle of the year. It started as an internal challenge to stimulate systematic thinking. The AIVD started posting it online in 2011. The intelligence agency doesn't use the puzzle to recruit, it's only meant for fun. It is compiled by people who work in the national office of connection security NVB in the AIVD. This department's main task is to secure state secrets, according to the broadcaster.

The puzzle is filled with brain teasers. One of last year's questions was: "DJT, FDMH and JMK were invited to a party, just like J-PS, JFS and BLF, YO, JMS and OH and BH. Who was left out?" The answer was BD - Bob Dylan. The question was about the presentation of the Nobel Prizes and the initials of the winners.

Over 1,250 people submitted answers to the Christmas puzzle of 2016. It was downloaded 100 thousand times, nearly twice as much as the 2015 edition.

The Christmas puzzle 2017 can be downloaded on the AIVD's website.