I’ve gotten those before. The funny thing is USPS doesn’t have my email address and I wasn’t expecting a package, so I knew it was a scam or a possible virus. BTW, I’m on a Mac. So I’m not that concerned about viruses, although Mac’s are still vulnerable to malware. I’m very careful anyway.
Prevent trojan cryptor attacks: Do not open attachments in phishing emails. Do not click links in phishing emails. Change RDP passwords. Beware of fake utilities and fake program updates. Do not click on malicious Flash content.
Keep all applications and operating system up to date.