The chat worm is called w32/Ramex and infected users will inadvertently send the worm to other users in their address books.
Skype users become infected after they download a link in a message and run the malicious software.
When a Skype user receives the chat message it includes an internet link. Instead of a .jpg image that it seems to point to, the link actually leads to a virus file.
By clicking on the link, the Windows Run/Save dialog box will pop up, asking for permission to save or run a .scr file. This is the virus file and should not be downloaded or run.
If the user accepts the file, their Windows PC will be infected with the w32/Ramex.A virus. The worm uses Skype's public Application Program Interface (API) to access the PC.
Security software firms F-Secure, Kaspersky Lab and Symantec have already updated their anti-virus products to detect and remove the worm.