Possession of child porn is not a strict liability offense. You still need to have the intent to possess whatever media is at issue and you must know what the media contains.
Now, it's easy for me to believe that if you can show affirmatively that you received child porn by accident, for example through the unknown-to-you malicious actions of others, the judge might let you off, but that's not actually encoded in the law; the federal agents you mention have an accurate view of things.
If you can show affirmatively that you received child porn by accident, the judge will let you off, because there wasn't any intent to possess child porn. Moreover, the prosecution will go after the person who sent the porn to you, and will likely recommend a good civil attorney for your lawsuit against that person.
Now, it's easy for me to believe that if you can show affirmatively that you received child porn by accident, for example through the unknown-to-you malicious actions of others, the judge might let you off, but that's not actually encoded in the law; the federal agents you mention have an accurate view of things.
If you can show affirmatively that you received child porn by accident, the judge will let you off, because there wasn't any intent to possess child porn. Moreover, the prosecution will go after the person who sent the porn to you, and will likely recommend a good civil attorney for your lawsuit against that person.