It's my understanding (but I'm not a legal expert) that if you were actually being served as a defendant in ANY legal action, you would be getting physical paper delivered to you one way or another.
Email legal summons? I don't think so.
Real law firm, fake spam email, real virus. See the Wall Street Journal article.
This might also be construed as a denial of service on the actual law firms phone lines . . . I can't imagine the pain those guys must be feeling as their phone rings off the hook.