I am sure that there are a lot more misdemeanours that go on that we never hear about.
It is all so easy to criticize but I am sure none of the past errant bank traders ever walked through the Human Resources Dept with a slogan 'I am a possible Rogue Trader' written large across their foreheads.
Nick Leeson - purported to have cost his employers millions: http://www.nickleeson.com/
Jerome Kerviel - purported to hace cost his employers billions:
http://www.huffingtonpost.com/2008/01/24/french-trader-singlehande_n_82993.html
So this trader is definitely not the worst offender:
Kweku Adoboli
http://www.bbc.co.uk/news/business-14939629
Pity they didn't put their brains, cunning and deviousness to good use but I do agree it is high time that banks started to bolt some doors.
Cali 
In this instance, assuming the story is much as has been reported, this guy is far from clever, he is in jail. Devious and dishonest on a large-scale is about all.
It is not so difficult for almost anyone in a position of trust, and responsibility, to alter records to conceal their activities. They work for the company, and internal security is usually weak, an often based on trust alone.
What is far more difficult, if not impossible, is to conceal something like this from the end of period audit. Figures presented by other external parties, i.e. those he was trading with, simply won't match UBS's own figures.
Presumably, their quarterly figures are soon to be prepared, and that is why he fessed up now, rather than sweat it for a few weeks and wait for them to discover his fraud.