i turned on target audience for my list and in "Target Audience" column i have such value: ;;;;Portal Owners, Portal Members, Group1. I thought that this is enouf to prevent user to see list item, but member of Group2 is still able to see it. What I'm missing?
There are a few steps. Here is a nice checklist:
I'll add that the Target Audience concept in SharePoint is a difficult thing to understand. It is almost easier to describe what it is not, rather than what it is. What it is not: a security mechanism. So what it does not do: prevent unauthorized users from seeing content (you must still rely on security trimming for that). In other words, its goal is to get certain content in front of certain audiences through the use of views if you will, but it does not prevent someone that is not part of that audience from viewing data in master list if they are otherwise part of a security group that allows it.
Many struggle to find the words to explain it. Some older but useful posts on the subject: