Every ad is scanned automatically before it goes live — including a link safety check completed within 24 hours (Google Safe Browsing). Ads are reviewed by a human only when the automated check rejects them, never as the default path to publish.
Links are not only checked once at activation — a link that turns dangerous after an ad has been running is caught by periodic re-scans and the ad is suspended immediately.
If an ad is withdrawn, the unused portion of its 365-day cycle is refunded on a pro-rata basis. This does not apply if the ad's link is later found to contain malware or a virus after it was first submitted and approved — that case is never eligible for a refund.