The spam crisis at PlusNet has taken its webmail service offline indefinitely after security auditors found unpatchable flaws in software provided by @Mail.
It has announced that it is replacing the offending software and has apologised to customers.
A service update (posted here) tells customers the emergency measures have been taken to guard against "minor vulnerabilities" which have not yet been exploited. PlusNet said it would provide details of plans to restore the service later today.
The closure follows a hacking attack on the BT-owned ISP, which saw customers' addresses and contacts bombarded with drug marketing. When PlusNet became aware of the attack last week, the webmail servers were immediately take offline, but returned to service after 90 minutes.
Neil Armstrong, product development director, told The Reg that PlusNet was working with police to trace the spammers, and will release more details of the investigation on Friday. The firm would not provide any details of the exploits which the attackers used, saying they were previously unknown, and it is working with @Mail. The @Mail webmail client is a white label POP3/IMAP software package for UNIX and Windows-based servers, popular with ISPs.
Some information around events which have caused the latest in a long run of email crises at PlusNet is beginning to emerge. An attack was launched last Wednesday which exploited a vulnerability in one of six webmail servers to load a botnet onto subscriber machines. The hole also allowed the hackers access to a list of customer email addresses and their contacts. PlusNet said it could not provide a figure for how many addresses had been stolen, but promised no other data had been taken.
Armstrong pointed to a legacy of underinvestment at the firm, which it copped to earlier this year on its BT-backed relaunch. He said: "That has changed now and it's worth knowing that this is a new vulnerability in a piece of third party software." ®