I moderate a yahoo group and members keep posting spam. How do I control spam being posted in the group?

it's not hackers cause this, it's more address book virus, send in members address book. going issue members of yahoo group.
spam filter on yahoo groups has never worked, , still doesn't.
can send post group of plan if members virus, remind members keep on virus protections, , can either set sending spam moderation or cant post-
locate said member members list- click edit membership below id- posting messages: override: member's posts moderated (edit) <-- click edit
next page choose either
* messages posted member not moderated.
* messages posted member moderated.
* member can't post messages.
click save changes

active members can rid of virus once they're aware it's happening. had school employee same virus. once fixed it, no spam them again, wouldn't remove active members.

these messages not show in spam folder @ all. group receives around 3 of these messages day, many.

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