Cheating is much easier than you might expect.Otherwise, why go to the extreme effort to cheat?
Step 1: Check obituaries for recently deceased.
Step 2: Check a phone book or online to find address of deceased.
Step 3: Use name & address online to find out if they're registered.
Step 4: Show up to their polling place to cast a vote in their name.
I could easily find this info in 5-10 minutes if I wanted to vote illegally. There are several million dead voters that are still on the voting rolls. We really have no idea how many people vote illegally, especially in states like California where things like this are encouraged.
What we really need is voter ID laws that require voter ID cards. Those cards could be easily deactivated whenever someone dies. That would greatly reduce cases of fraud, and it would also stop people from accidentally or intentionally voting more than once.