If I don't know any further details, I'll take it as if it were the best case scenario and someone found some irregularities and is fixing it. Irregularities doesn't mean something illegal happened, there are plenty of ways to siphon money out of a fund that don't break the law, that's what accountants are supposed to know and fix.
If something is blatantly illegal, follow the corporate policy and report as necessary to superiors and if that fails or is not feasible, authorities. Remain as anonymous as possible, do an anonymous report to HR or at least ask them to keep your identity concealed etc etc. And trust me, authorities don't give a shit about what is and isn't legal within a corporation, you file a report and nothing ever happens unless millions of dollars are going in the wrong (read: not in their) pockets. Even the corporation won't care if an accountant syphoned 100k to their personal bank account; they'll fire the dude/dudette and carry on because the bad press will hurt their stock/client base more than the 100k. For the 'regular' guy, $100k or even $1M is a LOT of money, within the billion dollar corporation this is chump change and well within their calculated losses.