I'll argue the opposite to popular opinion. Whilst I'm sure theres many cases where true actively suffering depressives turn to the internet as a remedy, based on annecdotal evidence, I'd postulate the link goes further.
Using a computer is staring into a lightbulb effectively. Hell, in some countries, that's deemed torture or "advanced interrogation technique". Yet we all subject ourselves to it. Anyone noticed how easy it is to stay awake beyond your usual capabilities when using a computer? In turn, theres a strong link between sleep deprivation or unusual sleep patterns and depression, or at least exasserbating pre-existing mild depression into something deeper.
Of course, I'm just referring to a PC here, and ignoring the internet. But, the internet plays its part by simply providing new content around the clock, and with no close time like TV or other digital media.