Your computer can possibly be attacked through the Ethernet wiring, but only when it is turned on. Rather than let a hacker have hours to work out the weak link in your machine, turn it off when you are not using it. They will perhaps try machine in Trinity. Manufacturers of software operating systems, e.g. Windows and Linux, issue security patches regularly. You must ensure your machine is patched up to date otherwise someone may come 'up the wire', or send an attachment, which will damage your machine.
Viruses are a blight.
All his files were corrupted. Virus scanning software is free within the University and simple to install, BUT requires you to be disciplined and run every attachment through it, rather than just double-clicking and viewing the attachment. Do not assume that virus scanners will do their job quietly in the background - you must use them explicitly to check files and disks. You can also take other steps to minimise the risk of virus damage. These steps are outlined below.