The vertical lines are a type of noise called 'grid noise' or 'read noise'. It is noise caused by 'dark current' in the electronics of the sensor and the camera's electronics that amplifies the analog signal from the sensor before it is converted to digital information. It is caused by electrical current that is not created by a photon striking a sensel (pixel well) on the image sensor, but is included in the sensor's readout as if it were.

There are other kinds of image noise in digital photographs, most notably "Poisson distribution" noise that is a result of the random distribution of photons in light due to the way light travels in waves instead of straight lines. This is often called 'photon shot noise' with regard to digital photography.

Read noise (or grid noise) is fairly constant in digital cameras. When there is plenty of light striking the sensor it is usually masked by the abundant light and is not detectable in images. When there is very little or no light striking the sensor it is much easier to see because the same amount of grid noise is not competing with much stronger signals created by brighter light. Changing the ISO setting of your camera changes the amount of amplification applied to the signal coming off the sensor. The signal caused by electrical 'dark current' is amplified along with the signal created by photons striking the sensor.

Poisson distribution noise (or shot noise) varies with the amount of light striking the sensor, but it varies with the square root of the change in the amount of light. It takes four times as much light striking the sensor to create twice as much shot noise. Thus, the brighter the image, the harder it is to see the shot noise because it, too, is masked by the stronger image signal created by the brighter light.

Taken together, both types of noise are most easily seen when a weak light source is amplified by a high ISO setting. The difference is that read noise usually stays in the same location from one shot to the next, while shot noise will appear randomly in various locations from frame to frame.

One way to avoid read noise is to shoot the scene with a brighter setting (more light, longer shutter time, etc.) and then reduce the brightness in post processing. This is very easy to do shooting still images in raw format. It's a little tougher with most cameras when shooting video unless your camera can output raw video.