Legal. There are a bunch of services that already do similar things, like SORBS and StopForumSpam -- you may want to look into these services, and others like them, before deciding to start your own. Source: almost 2 years ago

I want to object to your wording of this: got scammed on the Thinkpadforums recently by someone claiming to have one. It was NOT an active member of the Thinkpadforum, but some jerk/scammer who ONLY sent private messages to people looking for parts, hoping to make those people part with their money for nothing! That scammer (and others like him/her) was banned in no time and reported to http://stopforumspam.com/. Source: over 2 years ago

If you use a solid host like WPengine and a security app like wordfence.com it would be a very rare day indeed to get hacked. Source: about 1 year ago

If on wordpress, use the free version of wordfence.com to scan your site and identify possible viruses. Continue to use wordfence to protect the site, and if a successful business blossoms, consider the premium paid version. I'm not affiliated in any way, I've simply used the product with success for a number of years. Source: over 2 years ago

You can also read the documentation to learn about Wordfence's blocking tools, or visit wordfence.com to learn more about Wordfence. Source: over 2 years ago