Donohue said never expected anything like the sign hacking to occur.

'We've had the signs up for six years and we're phasing them out because we're bringing in flat screen monitors on the trains, so in another year it wouldn't have mattered,' he said.

Some detective work by a Canadian blogger may have discovered the identity of the hacker: a 24-year-old Canadian named Joshua, who talks about the incident on his MySpace page and has received kudos from friends for hacking the signs.

An e-mail to Joshua from Computerworld seeking comment went unanswered.