I logged in for the first time in a year and my level 3 skiller somehow became level 4

I logged in for the first time in a year and my level 3 skiller somehow became level 4. I had this skilled for like 4 years with some 99s and now I came back to check out what's going and its combat level is 4! It's totally ruined. I don't get it why and how. Was there some update related to this? My combat skills are all 1.

No, account wasn't hacked. When logged in it showed my IP from the last login and over 300 hundred days.

Also when logged in I appeared in the now ex-p2p zone above Falador to North-West in some new town.

So what the hell, why its level 4 suddenly if it was inactive for a year with combat skills all 1. Was there some kind of an update?

A little while ago, Jagex released an update called the Evolution of Combat. This update changed the entire combat system, including how combat levels are calculated. Your level 4 skiller with all level 1 combat stats now is the same as your level 3 skiller was before EoC.

Just elaborating on @murgatroid99's answer, the combat level formula changed with the release of the Evolution of Combat on 20 November 2012.

Currently, the combat formula is:

x + Defence + 2

Where x is your highest combat level (excluding prayer and Constitution).

For example, a player has 50 defence, 50 attack, 50 strength, 60 ranged, 60 magic, 99 prayer, 40 summoning and 99 constitution. The player's combat level will be:

60 + 50 + 2

Which equals 112.

In your example, you had all 1 combat skills (except 10 constitution). So now, you would have:

1 (highest cb skill) + 1 (defence) + 2

Which equals 4.