You wouldn't open your wallet to a known criminal. Why would you 'open' your computer, with all it's sensitive and personal data, to a cyber criminal? Not to mention giving them potential access to your friends and business aquaintences' computers through your email contacts!
A good way to view this common threat is by weighing the cost vs. the benefit. In other words, what do you gain by opening, reading and forwarding that email? What can you lose by doing such? In many cases, you stand to lose far more by becoming part of the email 'chain.' Protect yourself and your friends. "Just say 'DELETE!'"
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