UBE (Unsolicited Bulk Email)/Spam is blocked by the anti-spam service, and viruses are blocked by the anti-virus service.

Beyond that, spam is blocked based on it coming from spammers or advertising known spammer contact methods. These blocking methods can't be used for viruses. Virus emails typically come from innocent but infected hosts and not spammers. Additionally, they don't advertise known spammer contact methods. Usually the only way to determine that a virus infected email is a virus (and hence, unwanted) is by determining whether it contains a virus. As a result, the only way to block virus infected emails is by scanning it for viruses with the anti-virus service.

As a result, although virus email messages may be unwanted, they are not considered spam, and can typically only be blocked by signing up for our anti-virus service.

It is common in the anti-spam/anti-virus industry that they are separate services. Anti-virus service is typically billed separately as it does require more server resources and licensing fees for anti-virus software must be recouped.