serious help needed

I was in australia last yr and I commited a big mistake (sort of tax evasion I guess)which I learnt later abt and decided to leave the country before getting in trouble ,okie now a yr have gone by , my previous passport had expired , so I applied for a completly new passport with new last name new dob but with same first name . ANd applied for australian visa ,i didnt tolld anything abt my previous visit to aus also abt my old passport as i thought my visa will be refused and my new passport will be blacklisted too but now I am getting worried , plz guide me will they find out abt me , it seems illegal but have no other way,

thnx