Currently, the same service costs $2.95 per month, and there are approximately two million subscribers, said an AOL spokesperson. Although there will be a financial impact, in the long term we think this is where the company needs to be, he said.

The loss of almost $6 million revenue a quarter may be offset by a reduction in tech support costs and, the company hopes, declining subscriber churn as a maturing customer base gradually migrates to broadband services.

AOL says that almost one fifth of Internet users are currently infected with a virus. If the same proportion holds with AOL users, then helping clean four million virus-infected computers is arguably good for the health of the Internet too.