Click fraud is generally illegal under various federal and state laws in most jurisdictions (e.g., the U.S. Computer Fraud and Abuse Act and Wire Fraud statutes). It is definitely a crime to intentionally interfere with a competitor's business for financial gain.
However, suing the fraudsters directly is nearly impossible due to their anonymous, international nature. The most practical legal recourse is often to pursue a breach of contract claim against an Ad Agency, or if necessary, to push for a larger, documented refund from the ad network.
For a claim to be successful, you must have independent, forensic-level evidence (which is what third-party protection software provides) that goes beyond the data Google gives you. This evidence package is what a lawyer would use to compel a resolution.
