Ever sign up to be spammed? Probably not. But that’s effectively what happens if you open one unwanted email spotted this week.

The research team at McAfee spotted a unique spam specimen that adds a recipient to a number of spam lists, just after he or she opens it. That’s the only real purpose of the email: to verify an existing email account.

The unwanted email is also tricky because it pretends to thank the recipient for buying the Windows Vista Ultimate upgrade – a front for a PHP script that sends the spammer the victim’s email address.

The conventional wisdom applies: With email, if it looks too good to be true, don’t open it.