Q - tax deductibility - extended warranty and anti-virus software

We bought a new computer and with it an extended warranty (total 3 years = one year's manufacturer and 2 years extension with insurer), and a Norton anti-virus for 3 years.

We understand that we have to depreciate the computer for 4 years (straight line) - I think this is correct?

But, we are not sure if we can claim the costs of both the extended warranty and the anti-virus software in one year? Or, if we have to apportion the costs over the 3 years cover period?

Any thought or comment would be much appreciated!
Software used to be 100% written off in the first financial year of ownership.
Then it was changed to be depreciated over 2.5 years.
Currently, I believe, the effective life of in-house software for depreciation purposes was increased from 2.5 years to 4 years, enacting a measure contained in the 2008-09 Budget.

However, I'm not certain that you could say that anti-virus software was in-house? (perhaps it is?)
Thanks, Propertunity for your reply. I have searched in the ATO website, but could not find much guidance there. I will phone the ATO help line to get their views.