A security vulnerability have been identified with two models of Zyxel modems
Eir is contacting 130,000 of its customers to urge them to reset their modems amid security concerns.
It comes after a security vulnerability was identified with two broadband modems from manufacturer Zyxel: the D100 and P-660HN-T1A models.
German web users have also been impacted, Ars Technica reports, with hackers attempting to infect modems with the Mirai virus.
Eir says it has applied a security filter onto its network and pushed out an upgrade to the modem software.
Customers are also being advised to reset their devices, and the company is contacting those affected by letter and email to inform them of the situation.
In an online advisory, the company states: "We strongly recommend that customers with these modems change both their modem administration password as well as their WiFi password as soon as possible."
Details on resetting the modem can be found on the Eir website, while any concerned customers can also contact Eir on their 1901 helpline.