Ask Leo: Can Hackers See My Data?


By Leo Notenboom

I’ve heard that instant messages through AOL/Yahoo/MSN can be read by hackers that “sniff” the messages leaving my network. Is this true?


It’s actually true for all the data that comes and goes on your internet connection: web pages, emails, instant messaging conversations and more.

Most of the time it simply doesn’t matter. Honest.

On the other hand, there are definitely times and situations when you really do need to be careful.

Data traveling on a network such as the internet can be seen by many other
machines. Local machines connected via a hub, for example, all see the data
being sent to and from all the other machines connected to the same hub. As the
data travels across the internet, it actually travels across many devices each
of which can “see” the data.

Sounds scary.

The good news is that’s actually pretty hard to find data transmitted to and
from a specific machine unless you’re on the same network segment. For
example, if you’re connected to the internet via DSL, other machines sharing
that DSL connection might watch your traffic, but random machines out on the
internet would have an extremely difficult time tracking it down.

It’s not something I worry about much at home.

However, there are scenarios that you should be very aware of.

“… if you’re on the road you might simply wait until
you’re home to access sensitive sites like online banking or others.”
  • Wireless access points operate much like a hub. Any
    wireless adapter within range can see all of the network
    traffic in the area. Visited any open (meaning not WPA-encrypted) wireless
    hotspots lately? Anyone in the coffee shop or library, or even just outside on
    the street or a nearby building, could be sniffing your traffic.

  • Hotel or other third-party provided internet connections
    are also vulnerable, since you have no idea what, or who, is sharing or
    watching your connection. It’s possible that you’re on a hub, and the room next
    door or down the hall could be watching your traffic, or it’s possible that the
    hotel staff themselves are tapped into the internet traffic to and from all the

  • Landlord-provided internet connections, or those provided
    by or shared with a roommate or housemate fall into the same category: whomever
    set it up could very easily be watching the internet traffic going to and from
    the connection(s) that they provide you.

  • Your connection at work can also easily be monitored by
    your employer. In fact, the only difference between your employer and a hotel
    or landlord provided connection is that in most places the employer snooping on
    your use of their connection is legal, whereas the others typically are

  • What Can You Do?

    [This post is excerpted with Leo’s permission from his Ask Leo blog.]

    Leo Notenboom has been involved in the tech industry for nearly 30 years. After retiring from an 18 year career as a Microsoft Software Engineer Leo went on to create Ask Leo!, a free web site where he answers real questions from ordinary computer users.

    FaceBook URL: Leo’s Facebook

    Twitter URL:

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    16 thoughts on “Ask Leo: Can Hackers See My Data?

    1. With referenced to the “serious” poster, I think that the majority of people using the internet don’t understand the vulnerability of it. For instance, when they connect to the wireless internet in a hotel, depending on the network, it’s not only information that’s sent by email, etc. that’s vulnerable. Your entire computer maybe. I’ve been able to access other computer harddrives hooked up temporarily to the same network – not intentionally mind you – they’re just really easily seen and viewable when I’m looking for my own files. When people don’t set (or don’t know to set) the proper security protocols, there really are security / privacy concerns, so I think articles like this is useful the “general” user.

    2. Paretologic privicy software? They say their software overwrites information on your harddrive. Do you know if they are pulling our leg or if this software if really any good or not. I noticed you didn’t like Registry Cleaners so, this is making me wonder about privicy software too.

      I am very interested in your reply

    3. Finally, a serious poster (aka – Humor) sees this the same as I do (long time PC security expert)..a scare tactic aimed at less savvy users.
      Of course unsecured WAP or LAN’s in Hotels can have a risk associated with it, but your secure transactions with banks or https (encrypted) online shopping is still secure, and the chances that someone else is reading your emails or PM’s is highly remote at best.
      Now let’s talk about Registry Cleaners…..(LOL, let’s not and say we did Ok?), now there’s another scare sales tactic if we ever saw one. People have bought that one hook, line, & “we take MasterCard”.

    4. I have never responded to a pfish, but have had some scarry one. I have had Malware that required formatting my hard drive on Windows 98, XP and Vista. I’ve had more than one fraudulent charge on more than one credit card. I’ve had impersonation of my email that required getting a new email address. Right now something keeps turning off my firewall and virus scanner. None of the Malware and removal tools are detecting any problem. Could it be my wireless that I have never used? I have a message on my toolbar that says wireless is available, but when I go to the Console, Network shows no wirless is activated.

    5. As Humour says: “You may be able to see the TCP/IP layer communication between two machines (or more) and you may also be able to go as far as to disrupt the communication between the two machines, but actually obtaining the core content is a much more difficult exercise which less than 5% of the worlds computer users would be capable of achieving.”

      I agree, this is correct. I think the point here is, too many people of the “average user type” who do not understand what’s going on, have a false sense of security which we need to temper with the proper amount of cautiousness – for their own good.

    6. Humour speaks the truth, its more scaremongering than anything new. Every fascet of your lives has an element of danger. Walking the street, you can get mugged. Thieves will break into your house. Using the internet is no different, there are dangerous elements that can be suppressed quite easily.

      Asking how to go about fixing this, have your virus program up to date (AVG provide a perfectly usable free version for users and gain their money from companies to do this), have a trusted and well known spyware program such as Spybot S&D or Adaware fully up to date (both free). And then theres the common sense part, dont click ads, dont install rogue programs (a quick google should sort out the good ones from the bad) and do not leave sensitive information (like passwords/bank details) in plain text, in any electronic form and you should be fine to use the internet.

      Kinda like, when you lock your car in a public place, you dont leave your iPod and laptop in plain view.. its common sense to put them away. If in doubt, find a friend/relative who is computer savvy and ask them..

    7. humor,
      i take your point that it’s very difficult to decipher the data although traffic can be seen relatively easy, but your estimate of 5% who can successfully decipher data, when applied to 30 million windows users, says approximately 1.5 million people have a certain capability. by any standard, that’s a humongous pool in which hackers/devils reside. erieeeeeeeeeeeeeee!!!!

    8. Now I know this from personal experience. When I first got my Dell Inspiron E1505 Laptop computer. I was working in S.F. Ca., and the motor lodge I was staying at offered free wireless Internet access. And I got very upset with Dell and McAfee security when I found folders in ‘My Connections’ that did not belong to me or in my computer. There were so many and so much stuff that it was slowing my computer to the point it would hardly respond and then crash.
      Not only could I see other people’s folders in there, but I was able to click on the folders and open them too. Now at this point wireless connection was all new to me. But if I can open their folders, then it was likely they could do the same with mine.
      This was not acceptable at all. I no longer use the same security service (I don’t trust them.) But they did fix the issue by installing filters for securing wireless computers. I had did the research and found, that they had installed a security suite that is for a desktop computer. Which would be fine if I never travel outside my house and had it plugged into the router all the time.
      But there are ways to defend your computer. Microsoft does have lots of hits on this topic. You just have to look and not be lazy and wait for someone to do it for you.

      It is really too bad Castle Cops is no longer there. It was a great spot to learn about the security needed and how fix the things that got through the cracks. The people that volunteered to help folks in need were fantastic. And I doubt we will ever find them all in one spot like that again.

      But there are ways to defend your computer. Mirosoft does have lots of hits on this topic. You just have to look and not be lazy and wait for someone to do it for you.

    9. Perosnally I feel that although the article is stating the truth, it is nothing new, and they way it is written it is aiming to scare or raise awareness of the way the network layer has been designed to operate. In either case, its not educational enough in my mind and only serves to raise he type of responses seen from joe bloggs user as seen thus far.

      The fact is the network layer (TCP/IP) which is what the article refers to “loosely” is a structured mechanism to deliver messages “packets” from a machine in London too a machine in Sydney, per say, reliably without getting lost whilst travelling through the web.

      This method of communication is based on a set of rules which are defined by TCP/IP. Is it easy to see the packets at the TCP/IP layer? Yes, it is necessary infact in order to track and manage transmissions over a network. So anyone with the correct network tool will be able to view this information.

      However, the question should be; Is it easy to decipher the content of each message “packet” captured by the network tool? The 99% of the time the answer on this one is NO!

      The reason for this is simple. During the process of you logging in into a web based email account for example, anything from 30 to 100 packets are exchanged between your computer and the remote server. Each of these packets only contains a snippet of information which is in most cases scrambled/encrypted and on top of that at the network layer the content is displayed in Hexadecimal (computer language). So even if a network professional and or hacker is able to translate this single packet’s content, which coincidentally is not easy and does take time, if the content is encrypted, then the result he will get is going to be wrong. In simple terms, if you are trying to add 2+2 but the result you are given for that calculation is always 8, you unknowingly take this result as the correct value of, say a password for the sake of argument. You then may need to repeat the process up to 50 times, in order to string a set of results which combined will resemble the password of the individual, but, as you know, if a single value is wrong then its a failed exercise.

      So in simple terms, your next door neighbour, or the person sniffing out traffic from a room next door in a hotel would find it almost impossible to obtain any critical information.

      You may be able to see the TCP/IP layer communication between two machines (or more) and you may also be able to go as far as to disrupt the communication between the two machines, but actually obtaining the core content is a much more difficult exercise which less than 5% of the worlds computer users would be capable of achieving.

      By all means, protect your machines and do your best to stop any third party programs being installed on your machine with the intention of compromising your activities to a third party, but dotn worry so much about the network layer communicaton that has been happening for the past 3 decades.

      If things were that easy, banks etc. would not be offering their services online 😉

    10. Now the Internet has been around for some 30 years plus or minus and we still having problems with hacking and hackers having a ball doing whatever they choose; now what is the industry doing to protect the consumers/users that really do not know how to protect themselves?? Most pc users are not computer savvy and that means majority of us are just doomed and living in Lions Den. Many of us are willing to prevent this but do not know how. What are the specific suggestions or ways of preventing or stopping this scary mess???

    11. Can a landlord be watching the internet traffic with an ordinary PC?

      Can others watch the traffic, once I have finished my transactions?

      Is there any way to avoid watching the traffic if I’m on the same network segment?

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