Failed drive security

When an external hard drive that you used as backup with Time Machine for your iMac fails and you send it back for exchange how can you be sure that someone is not able to steal your identity off that drive? If all your information from your computer is on there, and, if there is a way to do data retrieval how can a person feel confident sending this drive to complete strangers for exchange? I recently drilled a hole through the piece of ■■■■ drive when i sent it back. WD did not like that.