A new vulnerability within the Gmail email account system, called Gmail Filter Virus, is currently affecting some Gmail users taking control of their account turning it into a virtual spam proxy.
Many Gmail account users will utilize the 'filters' feature for various automation functions in handling email messages. The Gmail Filter Virus specifically targets the filters settings by adding multiple filter rules for incoming mail messages. A Gmail account that has been attacked by the Gmail Filter Virus will automate a process to receive messages but skip the email inbox. It will then mark the messages received as read, forward them to recipients in your address book and then delete the message. Performing these steps will make it look like no message was ever received in your inbox and all trails of the message being sent to someone will be erased. Basically, Gmail Filter Virus acts as an email-laundering virus that covers its tracks.
The Figure 1 image below is an example of how a Gmail account's filter settings look in the event that it was attacked by the Gmail Filter Virus.
Figure 1. Gmail Filter Settings attacked by Gmail Filter Virus from PCMagazine
The origins of the Gmail Filter Virus are currently unknown, but we know that your own computer does not have to be infected with malware for this to happen. Some Gmail users who have encountered the Gmail Filter Virus may have used a public computer that was infected with some type of malware related to this virus and then proceeded to log into their Gmail account. From there, the Gmail account can come under attack. All it would take is logging into your Gmail account using an infected computer only one time.
Currently, nothing points to the Gmail Filter Virus being able to compromise your personal information but the recipients of email messages sent to your Gmail account could very well expose the contents of those emails.
Google presently knows of this vulnerability and already have server-side detections to attempt to block it. In some cases, the Gmail Filter Virus can still fall through the cracks. Unfortunately, we have not identified any security software that is able to detect the Gmail Filter Virus which can be best described as a vulnerability within Gmail account's filter setting instead of being an actual virus file.
In the event that you suspect your Gmail account may have the Gmail Filter Virus, you can simply check the 'Filter' option in 'Settings' to verify that the rules listed in Figure 1 are not similar to yours.