It's not illegal to hold an offshore account. It's only illegal if one doesn't declare the offshore income in one's annual tax return and pay tax at home.

Antipodean Machiavellis: Israel v Switzerland
For some, the secret world of Swiss banking hasn't been all it's cracked up to be. It reopened old wounds.
It wasn't hard to imagine that half the population of Sydney's eastern suburbs were frantically ringing their offshore accountants and lawyers this week.
· Rene's Swiss connection: Key Links [SMH]
· Swiss and Taxes