We don't touch or read Qur'an when we don't have wudu. On the other hand, we can recite it. Which ruling apply to reading Qur'an from a different medium than a printed book? Can we read Qur'an from internet when we don't have wudu, or should we do wudu before we read it through our computers?
Strictly speaking, the wudu requirement is for mus-hafs only. A mus-haf is a tangible copy of the Qur'an, something that is permanent. This requirement comes from the ayah in Surat Waqi'ah:79:
None touch it except the purified.
The scholars say that digital media doesn't count as mus-haf because it is a fleeting display that comes and goes, there is no perpetuity to the display of Qur'an on a screen.
Reference for assertion above: Answer by Shaykh Salih Munajjid and from other scholars.
Note this is only about permissibility, not about the etiquette or adab of reciting Qur'an. It is obviously desirable to recite Qur'an in a state of purity from both major and minor hadath (impurities).
I believe that the same rulings apply as when you read from a paper based Quran. We forget that either way the words of Allah are infront of the reader and deserve the same amount of respect.