The government hasn't formally acknowledged the internet shutdown.
As in past instances of country-wide internet blackouts, Iran is attempting to control both the protests themselves and the world's impression of what's going on. In theory, this reduces the chances of protesters organizing and posing a greater threat to the country's rulers. At the same time, it becomes that much harder to share news and illustrate the scope of the protests.
Unfortunately, this appears to be part of a larger trend around the world. Both India and Pakistan have shut down internet access in the hotly disputed territory of Kashmir in recent months, while Russia recently gave itself the power to shut down the internet at will. Internet shutdowns are quickly becoming weaponized, and that's unlikely to change as long as the leadership remains the same.