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Abstract

An emulation module (110) includes a pre-fetch queue (116) having an adjustable size (126) to eliminate any dependence of virus decryption routines on the size of the pre-fetch queue (116) when emulating executable files to test for the presence of virus infections. An executable file is tested by setting (210, 258) the size of the emulator's pre-fetch queue (116) and emulating (220) the file under the guidance of an emulation control module (130). Emulated instructions are monitored and a flag is set (230) when any instructions are modified (224) after being copied to the pre-fetch queue and subsequently executed (228). Emulation continues until the emulation control module (130) indicates (230) that the file should be scanned for virus signatures. If no virus signatures are detected (234) and the flag is set (244), the size of the pre-fetch queue is reduced (258) and the process is repeated. An executable file is declared virus-free (250) if the file is emulated (220) without setting the flag (230) and no virus signatures are detected (234). The executable file is declared virus-infected (240) when virus signatures are detected (234), independent of whether the flag is set (230). For Intel processors, pre-fetch queue sizes of 32, 16, 8, and zero bytes may be emulated.

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First Claim