Wow, Where are the old timers?
One of the older viruses/malware would redirect dial up just to collect termination fees. This script mailware was most often associated with porn sites., but not always. The frequency of this exploit tended to die down with growing broadband use over dialup. I first saw issues of this with dial up modems. My early cure for this as a prevention was tu use an Actiontech Dual PC modem connected to a router in the same configuration as a broadband modem and router setup.
This provided high immunity to the exploit as the modem contained the ISP dial up number and a compromised attack website could not log into the modem to change the numberr. As a network modem it did not respond to the Hayes AT command set.
A common practice for ohters was to change the escape charactor, but this only provided limited protection as a changed configuration file for common dialer programs could still be altered. Hidden and Read only attributes in DOS addad another defence with limited success.
Old school dial up was compromised by a very old attack against dial up modem use.