HLINK.DLL is not categorized as virus, worm, Trojan or backdoor. It is a vulnerability in the library HLINK.DLL, which is a DLL used by several Office applications, such as Excel.
Several proofs of concept that exploit this vulnerability in Excel have been made available. Additionally, code that actively exploits this vulnerability in Excel has been found.
Not only Excel files with XLS extension are prone to be exploited, but also other files with the following extensions: CSV, DIF, DQY, IQY, OQY, RQY, SLK, UXDC, XLA, XLB, XLC, XLD, XLK, XLL, XLM, XLSHTML, XLT, XLTHTML, XLV or XLW.
HLINK.DLL can be exploited by enticing users into opening a specially crafted document that contains malicious code. This document can be distributed using several methods, such as email, websites, network shares, etc.
If you have a Windows 2003/XP/2000 computer, it is recommendable to download and apply the security patch referred to the Hyperlink Object Library vulnerabilities, which are included in the security bulletin MS06-050. for this vulnerability. Click here to access the web page for downloading the patch.