BT may have inadvertently set up a war dialling resource for the opportunistic hacker, following the publication of around 5,000 private network dial-up numbers.

According to some information on news website Need to Know, BT has been publishing a number of private network dial ups as "internet service providers [ISPs]" if users have been connecting using a BT Together line.

Many businesses have private dial-up numbers to allow remote access to the company network. These numbers are almost always ex-directory, keeping network access points guarded from the prying eyes of hackers and war dialling software.

Unless, that is, one of the company's remote employees is dialling in over a BT Together line.

BT Together offers unlimited phone and internet calls at a flat rate. But the internet calls only apply to numbers in the 0844 04 bracket, i.e. BT SurfTime.

Policing these services against potential ISP abuse has apparently caused BT to start flagging any number that gets a lot of incoming BT Together data calls, such as the corporate network dial-in, as an ISP.

Not only does this mean that the user has to pay standard rates for the call, because it breaches BT Together's terms of usage, but the dial-in number gets listed on BT's publicly accessible ISP exclusion web page.

Need to Know said that there are currently around 5,000 such numbers on this list, many of which may be corporate network dial-ins, just waiting to be copied and pasted into some hacker's software toolkit.