In 2006 there was several raids in Germany, taking down dozens of Tor nodes (the Tor exit node) that were linked to Child Porn. Some (many) of these people were no doubt innocent of any child abuse charges, but their network would have been used to transmit the data via the tor network.
The effect on Tor was to massively disrupt the Tor network, slowing it down, and deterring people from using the server.
The long term effect of the raids was negligible, if anything, on child abuse, but it severely effected Tor, in the short and long term.
Were these raids a crack down on Tor or child abuse images?
Below are some articles from the time, relating to the issue: