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Protection from Dialers

Protect yourself against expensive dialers!

The Problem:
Certain Web sites will install dialer programs for Internet login onto your computer – sometimes openly but just as often surreptitiously. Worse yet, such programs usually reconfigure your system to use expensive 0190 numbers for standard login. The bad surprise comes with your next phone bill!

  • This danger is especially high for anyone using an operationalmodem orISDN board.
  • wever, evenDSL users aren't entirely safe, though DSL does not use standard dial-up login per se. But if an ISDN card or analog modem is being used along with DSL, 0190 numbers can still be dialed while a DSL connection remains active.
  • Nor areAOL members safe, as AOL clients have the option of accessing the online service via existing dial-up connections. Of course, these may also be set up to use 0190 or other expensive numbers for login. Aside from that, there is always the risk of a dialer establishing an 0190 connection independently from AOL.

The Solution:
cFosWatch can spare you such a bad surprise by checking the dial-up numbers of all your active DUN connections every 5 seconds. It will then compare those with a list of numbers whose dialup will result in immediate disconnection. A second list contains prefixes that will bring up a warning. If there is no reaction to this warning within 30 seconds, cFosWatch will automatically terminate such a connection as well.

By default, all0190 and0900 prefixes are disabled.
The warning list contains most numbers with 0180 or 0137 prefixes, since standard dial-up connection pricing has become much cheaper by comparison. Exceptions are those 01801 numbers that offer Internet access at less than 5 cents per minute as well as 01802 numbers charging a flat 6 cents per call. Likewise, international numbers (i.e., all numbers starting with '00') are by default included on the warning list.

Hidden 0190 numbers:
Assuming your Windows region setting is 'Germany' (i.e., country code 49), cFosWatch will also check whether dial-up numbers of call-by-call providers contain010xx or0100xx, which allows detection of "concealed"0190 numbers like 0103301 908xxxxx. For more on such "hidden" 0190 numbers, have a look at thisHeise News Ticker article.

Test it:
If you want to see for yourself how cFosWatch works, just add the number you typically use for dial-up login to one of the lists!

System requirements:
cFos employs TAPI for blocking 0190 numbers, which is integrated in both Win9x/ME and Win 2K/XP. However, using TAPI under Windows NT does require that you have at least Service Pack 3 installed. Windows versions before Win 98 may produce multiple warnings on RAS connections.

cFos user:
An important note for users of cFos (DSL/ISDN driver): cFosWatch is already included in cFos shareware and cFos/Professional versions 4.12 and higher. It can be configured during cFos setup. What's more, cFos also allows you to check connection numbers during dialup, which can either be set for Internet (pure HDLC) connections only or for all dial-up connections.


You "setup phone number blocking" under "configure cFos," where you can choose if you want to "deactivate" it, use it "only for Internet connections," or "for all cFos modems." You can also activate blocking of "all dial-up connections" there. "Double-check" enables phone-number checking regardless of whether you need to dial a prefix to get connected or not.

There are two settings for blocking phone numbers: The number can either be blocked immediately or you can be warned before it is being dialed.
Accordingly, you have two lists to choose from: "Phone numbers to block" and "phone numbers to be warned of."
Of course, you can add and delete numbers to and from these default lists as you see fit.

Register S117

This register allows you to set the properties of the phone number blocker as follows:

S117=1block phone numbers for HDLC only
S117=otheralways block phone numbers

Note: You can specify phone numbers in the [cfos] section of your CFOS.INI file (in the cFos directory) like this:


dialprefix=specifies what dial-out prefix (if any) is needed (e.g., often required by phone-switch setups)
dialblock=xxx,yyy,... contains a list of disabled prefixes (e.g., 0190)
dialwarn=xxx,yyy,... contains a list of prefixes that will bring up a window with a message warning you that they are being dialed. In case there is no user response, the connection will automatically be terminated after 15 seconds.

This feature may not be available for Win95.

What cFosWatch and cFos cannot prevent:

If you have an ISDN board or analog modem turned on, there is always a chance an 0190 number could be dialed. If this is not done using cFos or a DUN connection, the number can of course not be verified by cFosWatch. The only way to ward against such danger is to either purchase additional security/checking software, switch your modem off or pull the plug altogether. It almost goes without saying that calls from telephones and PCs that do not have cFos installed on them can – for obvious reasons – not be screened by cFosWatch either. To be on the safest of all sides, you may want to ask your local phone company to disable all 0190 numbers for your connection (though there is usually a special disconnection fee connected to that).
Furthermore, we assume no legal liability for any errors that might occur under cFos or cFosWatch; nor can we be held legally responsible for errors in other programs or underlying operating systems that may interfere with any of the security functions provided by cFosWatch. We also feel obliged to note in this context that there is no security program that cannot be deactivated or circumvented.

Have fun surfing the Web!