8. Is there a ban on anonymous donations to candidates?

Source 1: Article 64, paragraph 1, Political Parties Act 2013.  

Artículo 64 inciso 1°. – Las contribuciones privadas solo pueden acreditarse a favor de los partidos políticos.

Article 64, paragraph 1. – Private contributions can only be credited to political parties.

Source 2: Article 10, paragraph 6, Provisions for the Nomination of Non-Party Candidates in
the 2010 Legislative Elections

Artículo 10 inciso 6°.-  El origen y uso de los fondos empleados estarán sujetos a la fiscalización que la ley establezca.

Article 10, paragraph 6. 
The origin and use of the funds employed shall be subject to the oversight established by law.

Ley de Partidos: https://www.asamblea.gob.sv/sites/default/files/documents/decretos/2E597B83-D1C9-4C91-A9C9-6EC8A44FBA0F.pdf 
Regulación candidaturas no partidarias: https://www.asamblea.gob.sv/sites/default/files/documents/decretos/45E06ECC-27EC-49EC-B5D5-5D29814BAD32.pdf  

For independent (non-party) candidates, Article 10(6) of the 2010 Decree on the Nomination of Non-Party Candidates states that “the origin and use of funds shall be subject to the oversight established by law.” At the time of adoption, no specific law regulated political finance, creating a legal gap.
Since the enactment of the Political Parties Act (2013) and its regulations (2014), this Act has been interpreted as the law providing such oversight, filling the earlier gap.
Consequently, independent candidates are considered to be subject to the same criteria regarding the origin, use, and oversight of funds as those established for political parties. The Political Parties Act prohibits anonymous donations.
For party candidates, the provision does not apply directly, since only political parties may receive private contributions under Article 64 of the same Act.
In fact, by not regulating the financing of party candidates, the law creates a loophole that is exploited in practice by candidates to raise funds without being accountable to their parties or the electoral authority for the origin and destination of the funds received.