Adverts on Yahoo's homepage were infected with malware designed to mine the Bitcoin virtual currency, according to security experts.Malware Ads Served On Yahoo's European Home Page Aimed At Mining Bitcoins [bbc.co.uk]

Yahoo confirmed that for a four-day period in January, malware was served in ads on its homepage.

Experts estimate that as many as two million European users could have been hit.

Yahoo acknowledged the attack in a statement earlier this week.

"From December 31 to January 3 on our European sites, we served some advertisements that did not meet our editorial guidelines - specifically, they spread malware," the statement read.

It went on to say that users in America, Asia and Latin America weren't affected but did not specify how many European users were victims.