In our original paper (Section 4.4) we compared the ratios of hard X-ray to nuclear mid-infrared emission for Seyfert 1 and 2 (Sy1 and Sy2) nuclei, finding that both distributions appear significatively different according to the Kolmogorov-Smirnov test. We have detected a mistake in the computation of the X-ray luminosities (the lack of a 4π factor). Additionally, for two galaxies, the nuclear mid-infrared fluxes used within calculations are slightly different from the correct values which are reported in Table 3 of the original version. These mistakes affect the mentioned ratios of hard X-ray to nuclear mid-infrared emission, although they do not alter the result concerning the distributions, being statistically different. The correct values of these ratios are log(L Xintr/L MIR) = –0.21 ± 0.33 for the Seyfert 1 galaxies, and log(L Xintr/L MIR) = 0.17 ± 0.62 for the type 2 nuclei. Figure 8 has been updated with the newly computed values. We have also corrected the X-axis with respect to the original figure, which is now ν L ν. We have performed again Spearman's rank correlation test, finding that the correlation is significant when all galaxies and types 1 and 2 are considered separately. It is worthwhile to note that here we have excluded from the analysis two Seyfert 2 galaxies (NGC 1386 and NGC 7674) due to their extremely low hard X-ray luminosities, consistent with being optically thick sources. Recently, Horst et al. (2008) have estimated an intrinsic X-ray luminosity for NGC 7674 of log L Xintr = 44.56 erg s–1, in contrast to the non-absorption-corrected value reported by Lutz et al. (2004) (log LX obs = 41.91 erg s–1). Such a difference of about 2.5 dex corroborates our decision of not including these galaxies.