A method performed by data processing apparatus, the method comprising: receiving from a client device (110, 206) of a plurality of client devices a false digital component alert indicating that a digital component presented at a client device includes false information; receiving and storing attestation tokens from said plurality of client devices, said attestation tokens comprising: impression attestation tokens including impression data generated by the presentation of a digital component on a client device; and conversion attestation tokens including conversion data generated in response to detecting a user interaction for a digital component on a client device, wherein the attestation tokens are digitally signed and include the public key of the client device (110, 206); validating the false digital component alert by comparing a public key from the client device (110, 206) for the false digital component alert to a public key of the stored attestation tokens, verifying the digital signature of the attestation tokens, and determining that the digital component was actually presented to and/or interacted with by the user; in response to validating the false digital component alert, adding the false digital component alert to an aggregated report for the digital component; determining, based on a false alert ratio, that a magnitude of validated false digital component alerts in the aggregated report for the digital component meets a threshold; triggering a false digital component mitigation response based on the magnitude of the validated false digital component alerts meeting the threshold; and providing said false digital component mitigation response to one or more client devices. receiving from a client device (110, 206) of a plurality of client devices a false digital component alert indicating that a digital component presented at a client device includes false information; receiving and storing attestation tokens from said plurality of client devices, said attestation tokens comprising: impression attestation tokens including impression data generated by the presentation of a digital component on a client device; and conversion attestation tokens including conversion data generated in response to detecting a user interaction for a digital component on a client device, wherein the attestation tokens are digitally signed and include the public key of the client device (110, 206); impression attestation tokens including impression data generated by the presentation of a digital component on a client device; and conversion attestation tokens including conversion data generated in response to detecting a user interaction for a digital component on a client device, wherein the attestation tokens are digitally signed and include the public key of the client device (110, 206); validating the false digital component alert by comparing a public key from the client device (110, 206) for the false digital component alert to a public key of the stored attestation tokens, verifying the digital signature of the attestation tokens, and determining that the digital component was actually presented to and/or interacted with by the user; in response to validating the false digital component alert, adding the false digital component alert to an aggregated report for the digital component; determining, based on a false alert ratio, that a magnitude of validated false digital component alerts in the aggregated report for the digital component meets a threshold; triggering a false digital component mitigation response based on the magnitude of the validated false digital component alerts meeting the threshold; and providing said false digital component mitigation response to one or more client devices.