I came across this article written by Google's Webmaster which recommends setting/getting object parameters directly to improve code efficiency. However, I thought that doing as suggested (below) instead of accessing an object's properties through getter/setter methods) leaves the code vulnerable to attacks?
$rover = new dog();
$rover->name = 'rover';
echo $rover->name;
There is no "security" implication at all. Code isn't more or less secure in terms of attackers over the internet because it does or doesn't use setters or getters. They don't "protect" anything in terms of security. What encapsulation and access control in the form of getters/setters does is to protect you from stomping on your own feet accidentally. $rover->name = .. allows you to assign anything to the attribute any time. $rover->setName(..) allows you to do some error checking when setting a value, which you can use to nip bugs in the bud earlier. But it does not prevent bugs entirely, nor does it prevent an attacker from doing malicious things. An attacker isn't going to write code to assign something to your properties. An attacker exploits bugs in code or logic loopholes; not property assignments.
__setmagic method, there isn't really any way of stopping that, regardless of whether you use getters and setters.->name = .., just with the additional overhead of a function call.