I have an External HDD that I use to connect to a Windows OS (protected by Antivirus & similar tools).
If I connect it to my Ubuntu machine (which is not protected by any Antivirus tools) would it be a threat to my 900Gbs of files stored on my External Drive, after years of hardwork?
Though I've done a bit of research regarding this, I've not yet got a clear answer.
Please reassure a newbie to Ubuntu it is safe.
Viruses in the Linux world are, for all practical matters, non-existent. Unless you have valid reasons to believe that the Ubuntu machine you're going to use has been tampered with to destroy data in devices inserted in USB ports, you haven't nothing to worry about.
However, from your question it looks like (I might be wrong) you haven't any backup of the data files. If this is the case, you should do that ASAP: files can be damaged not only by viruses but also by disk crashes or human errors, such as deleting the wrong directory.
Linux users have much less concern with such things as viruses because Windows saturates the marketplace. There is little concern of your external HDD would pick up a virus when connecting to a linux OS. Also, data loss is not a concern as the Linux OS will show what is there just as in Windows explorer, but files will only be changed if you do the changing. I have a dual boot laptop (find myself using Ubuntu almost exclusively) and can see my Windows partitions at any time I wish from the Linux side within file manager. I have never had to be concerned with data loss in these partitions. If you are working with an external HDD, you would need to mount this drive before seeing, and each partition would have to be mounted (see man mount in a terminal). If this answer does not allay your concerns, my best advice is to not leave the external HDD on the system any longer than is necessary. Do what you wish to do with the external HDD and then umount and remove. Make the most of your copies (pics?) to minimize the time this external HDD is available.
I think that you are concerned to the point that no one or no information is going to allay your fears. Ubuntu does not need antivirus tools. Not necessary. Your Windows experience, which I understand being an extensive Windows user myself, has you convinced that accessing your Windows HDD from an Ubuntu system still would need antivirus protection. That being the case, your best bet is to not access this external HDD from Ubuntu to avoid your concerns, best solution to your problem.
Contrary to popular thought, malware in the Linux world does exist, but it's very very rare, and has to take advantages of elaborate vulnerabilities. In the Linux world, bigger threat is to servers, rather than desktop users: just as example, my server on Digital Ocean is being constantly attacked from variety IP addresses, but in all the time that I've had Ubuntu on my personal laptop - not a single threat.
Windows malware cannot take advantage of a Linux system, however, if you have wine, the Windows compatibility layer, there is a chance of Windows malware attempting at attacking your system.
The point is that you are 99.99% safe and sound on Ubuntu. If you do feel safer with antivirus , there are clam-av , tiger , all of which are installable through apt-get or Software Center. In all the time I've used Ubuntu thus far, I haven't heard of anyone using them , at least on a personal machine, and for myself there was no need thus far.
