Normally, firewalls at cellular carriers are your best friends, screening out malware before it ever touches your phone. University of Michigan computer science researchers have found that those first lines of defense could be your enemy through a new exploit. As long as a small piece of malware sits on a device, that handset can infer TCP data packet sequence numbers coming from the firewall and hijack a phone's internet traffic with phishing sites, fake messages or other rogue code. The trick works on at least 48 carriers that use firewalls from Check Point, Cisco, Juniper and other networking heavy hitters -- AT&T being one of those providers. Carriers can turn the sequences off, although there are consequences to that as well. The only surefire solution is to either run antivirus apps if you're on a mobile OS like Android or else to run a platform that doesn't allow running unsigned apps at all, like iOS or Windows Phone. Whether or not the exploit is a serious threat is still far from certain, but we'll get a better sense of the risk on May 22nd, when Z. Morley Mao and Zhiyun Qian step up to the podium at an IEEE security symposium and deliver their findings.