In February 2011, US software firm ITA Software ran a poster recruitment ad in Boston. It had a drawing of a brain seen from above, with the left hemisphere coloured red and with a label reading "Can you solve one of our puzzles?" and the right hemisphere coloured yellow and a label reading "Can you explain it to your mom?" The caption underneath read "We're hiring hackers with people skills." This incident is best known because of a photograph of the ad with a Post-It note attached by an unknown rider of Boston's transit system. The note read "MY MOM HAS A PHD IN MATH"