This indicates an attack attempt to exploit a Remote Code Injection vulnerability in MS Office Excel.
The vulnerability is due to user enable MACRO feature in MS office Excel while handling a malicious SLK file. A remote attacker can exploit this to execute arbitrary code on the target system via a crafted SLK file.
MS Office Excel
System Compromise: Remote attackers can gain control of vulnerable systems.
Disable MACRO feature in MS Office Excel by default.
Do not enable MACRO feature when handling Excel file from unknown source.