El Salvador blocked Telegram

On 15th September 2024, El Salvador blocked access to Telegram. On the same day, we rapidly responded by sharing relevant OONI data and our data analysis findings on social media.

The following chart aggregates OONI measurement coverage from the testing of Telegram in El Salvador between 15th August 2024 to 15th November 2024.

As is evident from the above chart, there is a spike in anomalous Telegram measurements on 15th September 2024, while all other measurements collected before and after this date show that Telegram was reachable in El Salvador. This suggests that Telegram was only inaccessible on 15th September 2024.

OONI’s Telegram test is designed to measure the reachability of Telegram’s app and web version within a tested network. The test attempts to establish a connection with a set of Telegram’s access points (endpoints), and annotates measurements as anomalous if connections to all tested access points fail. As we don’t measure all the possible endpoints of Telegram, we may miss some cases of blocking. We do, however, monitor an extensive list of endpoints (22 unique IP and port tuples), which is what allows us to infer the fact that there seems to be some amount of coordination around the block amongst some of the ISPs in El Salvador.

Specifically, we analyzed OONI data to examine the reachability of Telegram IPs in El Salvador by probe ASN and target. We found that access to Telegram was blocked on at least 5 networks in El Salvador (starting from around 4am UTC on 15th September 2024), with some ISPs blocking access to Telegram IPs, while others blocked access to Telegram by means of TLS interference (where the TLS handshake timed out right after the ClientHello message).

OONI data shows that the same Telegram endpoints were blocked by IP on AS17079 (Telemovil) and AS27773 (Millicom Cable), and that the blocking started at almost the same time on both networks, suggesting some kind of coordinated effort. Similarly, on AS14754 (Telecomunicaciones de Guatemala) we observe the same technique and that the block started at around the same time as the former ASes, but the list of blocked IPs seems to be more extensive than the ones targeted by AS17079 (Telemovil) and AS27773 (Millicom Cable). Both AS27903 (DigiCel) and AS263783 (Telefonica) blocked Telegram by means of TLS interference, but AS263783 appears to have started performing IP based blocking too, starting from around 14:00 UTC on 15th September 2024.

According to OONI data, access to Telegram was restored on all 5 networks in El Salvador on 16th September 2024, as illustrated above.

This blocking event resulted in a significant OONI measurement spike in El Salvador on 15th September 2024, as well as in ongoing measurement coverage thereafter -- suggesting increased OONI Probe adoption and use of automated testing following the block. This will enable us and the global internet freedom community to more effectively monitor future blocks in El Salvador.

If you are in El Salvador, you can help contribute more measurements by running OONI Probe.