The FBI has set a new challenge for codebreakers. Amongst all the serious stuff on its site like lists of the most wanted fugitives you'll find a dot code puzzle  just waiting to be solved.

To interest the public in the work of its Cryptanalysis and Racketeering Records Unit (CRRU), the FBI has devised a dot code cryptanalysis puzzle. It looks a bit different to other coded messages, in fact you might just see it as and attractive arrangement of dots a a grid until you notice that they are grouped into sets of patterns - words.

The message can then be be cracked in the same way as other simple ciphers, by working out which repeating code corresponds to which letter of the alphabet using frequencies of letters and letter pairs.

One hint is to look for the one-character and two-character words and other helpful advice can be found in an article “Analysis of Criminal Codes and Ciphers” from the FBI's publication Forensic Science Communications.

If you like this type of puzzle and have never considered www.fbi.gov as a likely source then there's a treat in store.  As well as this puzzle there are four previous ones. If you are stumped by the latest one try cracking the November 2007 code first - the web page it references no longer exists but what would you expect after more than 5 years.

The answer to the 2013 puzzle is given on the FBI site so we are not going to give it away here.