How do I create this effect from the Doctor Who episode 'The Bells Of Saint John'?

It's the hacking text which flies in and out when the characters are hacking.

How do I create the scrambling effect where the text scrambles itself before showing the actual code?

More importantly, do I just need to make it look super code-ish or do I just have to type in some random alphanumeric gibberish with some symbols to make it look nice?