Single-pass zero is sufficient for most anything - unless your site security officer or HIPAA officer tells you otherwise and requires multi-pass pattern overwrites, and if you don't have or know what an SSO or HIPPA is - then single-pass zero erasure is just fine.
As for your question, it's answered in the man page:
secureErase [freespace] level device
Securely erase a disk or freespace on a mounted volume.
Ownership of the affected disk is required.
Level should be one of the following:
o 1 - Single pass randomly erase the disk.
o 2 - US DoD 7 pass secure erase.
o 3 - Gutmann algorithm 35 pass secure erase.
If you're dealing with floppy disks or disks from the megabyte era, then positioning was a little sloppy and you could pick off data by mis-positioning the heads. These days? Barring a really valuable target, the likelihood that anyone would fund the recovery effort from a single-pass erase is unlikely.
And data in the bad blocks generally won't get zonked, regardless.
On the other hand, if you're storing anything that could lead to public embarrassment or legal action or Elvis's home telephone number or such, you might want to just slag the disk.
