BT-owned telco Plusnet has blamed subscribers who use third-party routers for a rise in hostile DNS traffic that has been crashing its way through the ISP's system.
The rebuff came after Sheffield-based Plusnet suffered a nasty outage last Tuesday relating to an unspecified "network error".
A Reg reader claimed on Sunday, in the comments section of our story last week, that Plusnet's servers were "once again, directing requests for popular websites to the same phishing website they were directing them to on Tuesday night."
We put the allegation to Plusnet. Your correspondent notes the firm is quite sluggish when it comes to responding to press inquiries through the normal channels.
The ISP said:
Since last week, we’ve seen an increase in the amount of malicious DNS traffic being directed through to Plusnet IP ranges.
It appears that some of our customers, (and no doubt a number of other people out on the internet) running TP-Link, Linksys and Edimax routers have been compromised due a vulnerability which appears to allow the allocated DNS server in the router to be changed.
This means requests to domains like Facebook or Google are being redirected on ALL devices behind the router to a website which contains a malicious payload disguised as a Flash update.
Plusnet pointed out that Bracknell-based telco Andrews & Arnold had also reported a similar issue to its customers. It said that "this type of attack is called Pharming. In short, it means that any internet traffic could be redirected to servers controlled by the attacker."
A&A advised subscribers to either scrap the affected routers, or else change the DNS settings back to auto. It added that "changing the administrator password and disabling WAN side access to the router may also prevent this from happening again."
Plusnet similarly recommended that its customers check the security settings on their devices.
"To be clear, the routers Plusnet provide aren’t vulnerable to this hijack. These are third party routers purchased by the customers themselves," a spokeswoman at the firm added.
The advice from the ISPs came in light of security research group Team Cymru spotting an attack earlier this month that, it was estimated, could have redirected as many as 300,000 devices to a malicious resolver. ®