Partial match: Antisocial (2013).
From the reviews on IMDb:
A satire like Dead Set.
Apparently, a social media site uses subliminal to draw members back. Unfortunately, that program mutates into a virus that affects human brains. Turning people delusional and violence. To the point where a tumour grows and some heads explode.
Lots' of frights and gore. As usual, the survivors barricade themselves in a house and fall one by one. As the survivors frantically check the social site for news, they are infected too.
The time of release matches, as do the exploding heads and worldwide contagion, but the opening scene is not set in a forest. Haven't checked the whole movie, but it's still possible there's a forest scene later on.
Warning: trailer is NSFW (gore, woman in underwear):
Found with the Google query
science fiction movie virus head explodes site:imdb.com/title, page 2 of the results.