App Store anti-virus apps can't really hurt anything, as long as you never let them delete anything they find. (That's a good general rule for all anti-virus software.) So, although I don't really respect Kaspersky, keeping that app isn't doing you any harm, as long as you use it properly and aren't assuming that its use it keeping you safe.
As for what else to use instead, it's important to understand that no anti-virus software would be able to guarantee that you won't have a recurrence of this event. Most anti-virus software doesn't recognize most adware at all. One may detect one adware program, while another may detect a different one. There's just no consistency in this area. Fortunately, adware is very easy to avoid if you're careful about what you download.
For more information on this, see my Mac Malware Guide.
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