Snathi are a minor race in the base game.

The Revenge of the Snathi are a major race available through DLC (includes some kind of campaign for them).

The Arceans (and the Torians) are only available if you have the Mercenaries Expansion.  Sadly, you cannot disable Mercenaries without disabling these races as well.

If you mean that you don't see them listed with the other races included in the base game when you are choosing a race to play, it is because they don't display with them.  For some reason the display order is this:

1.   The races in the base game.
2.   All races added by mods.
3.   Races added by DLC and the expansion pack, such as Snathi Revenge, Torians, Arceans and United Earth.
4.   All custom factions.

You need to scroll down through the list until you get to the races added by DLC and the expansion pack.  They are listed together.

When you are adding factions to play against, the DLC and expansion races are mixed in with the mod races and custom factions.  You need to scroll through the list until you find one you want.  They are not listed together, so if you want another one you have to keep scrolling.  They are easy to miss, so you may have to scroll up and down until you find the one you want.

Not to hijack the thread, but I've been using Kaspersky for years now and have never had a problem with it - they really produce a great product.