Cisco's Security blog reports that LinkedIn was responsible for over a quarter of all the spam caught by the company's systems for a span of 15-minute last Monday. Spam from the Web site also accounted for about 15% of all spam messages for the day.

The messages usually come from strangers and alerts users that they have "2 messages awaiting your response."

The Cisco blog says that the attack is extreme due to its ferocity and its focus on business users. Once users click on the link, a trojan virus gain access to the PC, which searches for bank account numbers and passwords.

The link leads to a page that tells users to "PLEASE WAITING... 4 SECONDS." Users are then lead to the Google homepage instead of the LinkedIn page.

The attack is regularly modified, keeping one step ahead of anti-virus vendors that are trying to provide a fix. To keep away from the attacks, users are advised to use website evaluation services such as AVG's LinkScanner, that analyzes a Web site before allowing the browser to load content.