Thread Safety of a Sample Function

Trend Micro's endpoint scanning engine runs many worker threads in parallel, each one scanning files and recording signature hits into a shared cache. Here is the cache class as it's currently implemented.

public class ScanResultCache {
    private Map<String, Integer> hitCounts = new HashMap<>();
    private int totalScans = 0;

    public void recordHit(String signatureId) {
        if (hitCounts.containsKey(signatureId)) {
            int current = hitCounts.get(signatureId);
            hitCounts.put(signatureId, current + 1);
        } else {
            hitCounts.put(signatureId, 1);
        }
        totalScans++;
    }

    public int getTotalScans() {
        return totalScans;
    }

    public int getHitCount(String signatureId) {
        return hitCounts.getOrDefault(signatureId, 0);
    }
}

A single instance of ScanResultCache is shared across all scanning worker threads. Is this class thread-safe? Explain exactly why or why not, referencing specific lines, and describe what you would change to make it safe for concurrent use.