Many vendors have provided in the cloud AV scanning for many years. The AV vendors are now looking to move torwards a more cloud solution as they are realising two things;
1) customers are understanding cloud security and the adoption of SaaS (Software as a Service filtering) is growing at such a pace vendors are running to catchup with what customers are wanting.
2) the majority of threats now come from the internet, with a high % coming over web HTTP rather than email SMTP. Therefore scanning the protocol in the cloud not only fights the malware at its source, it also provides the customer more effective filtering (the independent cloud vendors can blend multiple AV technologies compared to pure play AV vendors who are tied to their own engine). An AV vendor will only use their only AV engine so moving it to the cloud doesnt compete with an independent vendor offering a multiple AV scanning approach.

Also a service in the cloud is able to offer SLA (Service Level Agreements) to the protection levels provided. For example Webroot offers 100% protection guaranteed against known and unknown email viruses.

Source: http://www.webroot.com/En_US/business...

Jaytop
You should look at www.anubisnetworks.com - very popular with service providers but you can licence directly.

You need to validate how far the AV solution is truly utilising the cloud and how much is marketing hype.

Some of the cloud Av products still claim a100MB+ client install for example !

Checkout Prevx at 1mb client install as an example of what can be achieved.

Source: http://www.prevx.com/