Yes, a hacker may walk away with just an address book. The more frightening question is… what else could the hacker access?
Let me start with the technician’s answer.
Personally, I’m not satisfied with what that person said. This answer could mean a couple of things (I’ll talk about at least one of those here in a minute).
First, how did the technician determine that the hacker took a copy of your address book? More specifically, if that happened, how could the technician say that your security held? If the hacker accessed your address book, then some part of your security clearly failed.
Second, I can’t think of a scenario where a hacker could gain access to only your address book and nothing else. It doesn’t matter how they did it. Accessing your address book is just as easy as getting at anything else on your computer.
Now, the hacker could choose to only take your address book. Maybe it’s the only thing of value to this particular hacker. But you don’t know what the hacker did or didn’t do. You have to look at the bottom line: could the hacker have accessed other private information on your computer if he (or she) grabbed your address book?
The answer is almost certainly yes.
The other part of this depends on what you use to check email. You don’t mention in your question if you’re running an email program on your computer (like Thunderbird, Outlook, or Windows Live Mail), or accessing email through a web interface (like Gmail, Outlook.com, or any ISP-based web email interfaces).
Based on what the technician said, I’m assuming that you access email through a web interface. In that case, the problem didn’t happen on your computer because the hacker accessed your online email account. For example, the hacker simply accessed your Hotmail account online. Your computer could be just fine because it wasn’t hacked and its security wasn’t compromised.
Nonetheless, if a hacker has access to your Hotmail account or your other online accounts, is that person only limited to just taking your contacts?
The answer is no.
Hackers and linked accounts
A hacker can do a lot more, especially if you linked your email account with other services. Your Gmail account could be linked to the Picasa file sharing service or the Google+ social media site. In that case, they have access to your files and social feed. If you linked your Hotmail account with SkyDrive and you have files stored there, they can access those. With so many inter-connected services these days, I simply can’t see a way for a hacker to be limited to only your contacts or address book.
The bottom line is that I’m not really in agreement with the fundamental statement that the technician is making. It’s possible that your computer wasn’t touched. I suspect that’s what he really meant. Still, there’s a hole in your security.
It may be just a personal hole. Perhaps you’re using a simple password, maybe you’re not using open WiFi correctly, or any number of different things that could allow a hacker to hack into your online account. The best thing to do is to simply review all of the things that are very important in keeping your internet access, your accounts, and your computer safe.