OllyDbg is a single-process, multi-thread code-level debugger for 32-bit programs running under Windows 95, Windows 98, Windows NT and Windows 2000. It allows you to debug and patch executable files in PE (Portable Executable) format. "Code-level" here means that you work directly with low-level bits, bytes and processor commands. OllyDbg uses only documented Win32 API calls, so the chances are good that you will be able to use it on the next derivatives of 32-bit Windows operating systems.

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