Ouch...that sucks...this is why it's very important to have an up-to-date AntiVirus and Firewall program. My recommendation is Comodo Firewall and Comodo Antivirus (google them). These are by far the most updated Internet security programs I've used and they're completely free. Sidenote: you might want to check all settings for Comodo Firewall, as it can scan files in the cloud, which if you're on a data cap, could cause some unnecessary usage. My secondary recommendations are AVG and Avast, both are free and do a decent job. Disclaimer I'm in no way trying to push Comodo/AVG/Avast, I genuinely use Comodo and recommend it to anyone that's looking for a free AV.

Edit: Nevermind I read that you were already using an AV and firewall...