if your coputer gets seized in any type of 'raid' my advice owuld be to call a lawyer immediately LOL
as for what can and cant be disclosed.. basically anything that is nothing to do with the basics of the case are inadmissable in court therefore they should never see the light of day however, if you have 'illegal' materials on your machine then they can use that as evidence and will most likely use it on fresh charges.
once law officers execute a search + seizure warrant any evidence they feel is required to press charges may be used for either the original charges of why the warrant was executed or, can be used as evidence in any further charges even if the evidence was found by luck in relation to a previously existing charge basically, call a lawyer and get 100% sound legal advice
