The Google AdSense 120×240 – Vertical Banner is a shorter version of the 120 x 600 – Skyscraper. The AdSense version of this ad unit is only available for text ads, due to the small area. Once again, the 120 x 240 – Vertical Banner ad unit size is also used by Microsoft Advertising, while it has been delisted by the IAB (Interactive Advertising Bureau).
This small, vertical banner is ideal when you have a small area under a thin column or you have a small area available in a large header or footer. While the 120 x 240 – Vertical Banner shouldn’t be relied upon as your main income generator for a page, as it doesn’t attract a lot of attention, it can be very effective if placed correctly. If you’re trying to place a skyscraper under a menu or in a sidebar and it is just too long, the 120×240 vertical banner is a good alternative.