Internet and mobile security provider AVG technologies warns that vishing is on the rise against users of Skype. In a typical vishing scenario, while online, users receive automated voice messages via Skype saying their PCs have been checked for viruses and that a "fatal virus" was found. The message then advises them to repair the problem and provides a link to a malicious website.

The aim of the criminals is to get their victims to download to their computers malicious software disguised as security updates or antivirus programs. The ultimate goal of vishing is often to scam users into providing personal information that can be used to break into financial, social networking and other online accounts.

“While Skype works hard to prevent these kinds of attacks, users need to be vigilant. Although many users have learned how to spot and resist suspect e-mails and Internet chat messages, we aren’t conditioned to be as wary of phone calls," said Tony Anscombe, ambassador for Free Products at AVG. "With land lines and mobile phone calls, all contact with unwanted callers can be cut simply by hanging up. But because Skype calls are placed over an Internet connection, once the digital connection is established, it can be used as an open conduit regardless of whether you’re participating in an online call or not.”

Anscombe’s advice is to hang up immediately on the Skype call, block the user and report the user for abuse. By reporting abuse by the user, Skype's automated systems for blocking malicious users will be updated and this will help to protect the greater Skype community.  Additionally, don’t accept calls from unfamiliar sources and don't follow any instructions from suspicious parties.

As a preventative measure, users should lock down their Skype account settings as follows:

Open Skype and click on the "Skype" tab to view the drop down menu.

Click on the "Privacy" option and the "Skype — Options" panel should pop-up.

The "Privacy settings" tab should already be open, but if not click on it.

Click on the "Show advanced options" button.

Under "Allow calls from…" click on the "People in my Contact list only" button.

Under "Automatically receive video and screen shots from…" click on either the "People in my Contact list only" or "No one" buttons.

Under "Show that I have video to…" click on the "People in my Contact list only" or "No one" buttons.

Then click on the "Calls" tab.

Click on the "Show advanced options" button.

Under "Allow calls from…" click on the "People in my Contact list only" button.

Make sure the "Answer incoming calls automatically" check box is NOT checked.

Click on the "IM & SMS" tab.

Click on the "Show advanced options" button.

Under "Allow IMs from…" click on the "People in my Contact list only" button.

Last, but most importantly,  click on the "Save" button at the bottom right of the panel.

If for some reason it is not practical to only accept calls from known contacts, ensure the "Answer incoming calls automatically" option is not selected, as described above, to retain the option of denying calls from suspicious sources.