Biggest number ever factorised

Multiplying two numbers together is easy. Much harder is the task of splitting a number into its "factors" – two smaller numbers that multiply to give the original number. Factorisation is useful in deciphering certain codes, where the two factors of a code’s "key" number are needed to decipher an encrypted message. The difficulty in factorising the key is then what makes the code secure. The biggest encryption key factorised to date is 232 digits long. It was split into its factors in 2009 by an international team from six research institutes, led by Thorsten Kleinjung, of the École Polytechnique Fédérale de Lausanne, Switzerland. Their calculation took three years on hundreds of networked PCs, – it would have taken 2,000 years on a single machine.