SSDs are, in fact immune to magnets and most newer computer (primary) drives are SSD for various reasons. Spinning HDs can be very vulnerable to magnetic forces (commercial drive destruction employs a magnetic degaussing process to erase data). The trick is that the magnetic needs to be in the correct position to impact the spinning platters. Interesting fact that most, if not all, spinning HDs incorporate small, very strong, rare earth magnets to operate the drive’s read/write heads. Again, positioning of theses magnets are the key to their success. As for positioning a magnet on or near your computer or external HDD, do so at your own peril.