Australia leads showing as "open email"

Is anyone else seeing that their Australia leads are showing as "opening" emails but are not actually opening them? Some of our internal team members are in Australia and we send them certain communications from Marketo. They are saying that they've never received the email but in Marketo it is showing as "open." Someone mentioned in Australia it is common to have software that "opens" emails for you for security reasons. Is anyone else seeing this?