The rise of digital communication has provided a veil of anonymity for those seeking to harass, intimidate, or threaten others. In the Philippines, receiving a threatening text message from an unknown number is not merely a nuisance; it is a legal matter that triggers various penal laws and procedural rules.

1. The Primary Offense: Grave Threats and Light Threats

Under the Revised Penal Code (RPC), threatening another with a wrong amounting to a crime is punishable.

Grave Threats (Article 282): This occurs when a person threatens another with the infliction of a wrong amounting to a crime (e.g., murder, physical injuries, kidnapping). If the threat is made through a text message, it is considered a threat made in writing.
Light Threats (Article 285): This involves threats that do not amount to a crime but still cause fear or disturbance, or threats made during a heated argument that the perpetrator does not persist in.

2. The Cybercrime Prevention Act of 2012 (R.A. 10175)

Section 6 of Republic Act No. 10175 provides that all crimes defined and penalized by the Revised Penal Code, if committed by, through, and with the use of information and communications technologies (ICT), shall be imposed a penalty one degree higher than that provided for by the RPC.

Because text messaging utilizes telecommunications networks and mobile devices, a "Grave Threat" sent via SMS is elevated to a cybercrime, carrying significantly heavier penalties.

3. The Challenge of Unidentified Persons (John Does)

The most significant hurdle in legal action is the anonymity of the sender. To file a formal criminal complaint, the identity of the perpetrator is usually required. However, Philippine law provides mechanisms to bridge this gap:

SIM Registration Act (R.A. 11934): This law mandates the registration of all SIM cards. In theory, every mobile number is now linked to a verified identity. Law enforcement agencies can request the disclosure of subscriber information from Telecommunications Entities (PTEs) during an investigation.
The "John Doe" Complaint: A complaint can initially be filed against a "John Doe." Law enforcement agencies, such as the PNP Anti-Cybercrime Group (PNP-ACG) or the NBI Cybercrime Division, then use the complaint to initiate a formal investigation.

4. Steps in Pursuing Legal Action

A. Evidence Preservation

Do not delete the messages. The digital evidence must be preserved to maintain its integrity.

Screenshots: Take clear screenshots of the message, including the sender’s number and the timestamp.
Context: Keep the entire conversation thread to show the sequence of events.
Technical Data: Avoid "rooting" or "jailbreaking" the phone, as this might complicate the authentication of the digital evidence in court.

B. Police Blotter and Investigation

Report the incident to the nearest police station to have it recorded in the blotter. Subsequently, approach specialized units like the PNP-ACG. They have the technical capability to coordinate with telcos to trace the origin of the message.

C. Requesting Data (Warrant to Disclose Computer Data)

Under the Rule on Cybercrime Warrants, law enforcement can apply for a Warrant to Disclose Computer Data (WDCD). This legally compels a service provider to release the registration details associated with the offending SIM card.

D. Filing the Complaint

Once the identity of the sender is established through investigation, the "John Doe" status is replaced with the person’s actual name, and a formal preliminary investigation is conducted by the Prosecutor's Office.

5. Other Applicable Laws

Safe Spaces Act (R.A. 11313): If the threatening messages include gender-based sexual harassment (misogynistic, transphobic, or sexist slurs), the perpetrator can also be charged under this law, which specifically covers "gender-based online sexual harassment."
Unjust Vexation: If the messages do not contain a specific threat but are intended to annoy, irritate, or vex the victim, the sender may be liable for Unjust Vexation under the RPC.

6. Civil Liability

Beyond criminal charges, the victim can file a separate civil action for Damages (Article 19, 20, and 21 of the Civil Code). This allows the victim to seek compensation for moral damages (mental anguish, fright, and anxiety) caused by the threatening messages.

Legal Note: In the Philippines, the "Chain of Custody" for digital evidence is crucial. For a text message to be admissible in court, it must often be authenticated following the Rules on Electronic Evidence, ensuring that the message shown to the judge is the exact one received without alteration.