From what I can gather, people are using the "upload your contact list" / "connect to your email account" feature, without realizing that it automatically sends out invites to your contacts. I'm pretty sure it spells that out quite plainly, though; at least I vaguely recall that it did last time I decided not to use the feature.
Yep. That's what it says. I for one had selected some 7 contacts (me stupid had allowed access to my address book). Carefully selected. A give-away was already, that there was no 'deselect all'; only 'select all', and I had automatically 153 contacts pre-selected. What a fun, without a 'deselect all'. So I deselected some 146, one by one. 7 left. And me scrolling to double-check if they were the good ones. So I selected 7. Do you know how many were sent? 584.
Another give-away of LinkedIn malicious undertaking:
1. I never had to confirm those invites being sent.
2. (Worse) There is no way to retract invites not yet being opened or answered. No 'cancel all my invites'
Now it's your turn to show any 'best practices' by LinkedIn to me.