64bit memory address won't fit in Win32(64?)'s API WriteProcessMemory?

Firstly, whenever you have problems with WINAPI, you should use GetLastError to find the * specific* error.

Firstly, whenever you have problems with WINAPI, you should use GetLastError to find the * specific* error. In this case, I'm pretty sure you lack debug privileges, so the OS is denying write permissions, see AdjustTokenPrivilages and this example, you want SE_DEBUG_NAME privilege. However, it should be noted that you should never use a fixed virtual address (0xA4283C508C in your case), as most programs will be relocated, invalidating your address (either due to ASLR, code page overlaps or jsut a pure lack of a preferred load address).

You only need debug privilege to open handles to processes that run under a different user. – pezcode Oct 13 at 10:17 @pezcode: no, you need it to open handles to programs that require administrative or debug privileges (or anything else you don't have the privileges to currently access), this is why ring3 debuggers are required to run in admin mode, so they can access protected process memory. Maybe you should read up on access control: msdn.microsoft.Com/en-us/library/windows/desktop/… – Necrolis Oct 13 at 10:33 ring3 debuggers work on non-admin accounts just fine, as long as you don't try to attach to a process of another user (that includes SYSTEM).

If you had browsed that link yourself, you would have found this page: msdn.microsoft. Com/en-us/library/windows/desktop/… And another one: support.microsoft.Com/kb/131065/en-us – pezcode Oct 13 at 10:48.