According to the ETA and Home Affairs websites: "If you have a criminal conviction and have been sentenced to a term of imprisonment of 12 months or more, you should not be applying for an ETA. You might be eligible to apply for other types of online visitor visas."

So unless you were sentenced to 12 months or more in prison you're ok to get an ETA. But perhaps best to check with the Department of Immigration or Home Affairs directly to clarify.