In the warning, the US National Infrastructure Protection Center (NIPC), the cybersecurity arm of the US Federal Bureau of Investigation (FBI), cautioned that "wide-scale hacker attacks against US Web sites and Internet Service Providers are being planned for later tonight [5 August], possibly emanating from Western Europe".
The agency cited "credible, but non-specific" information as the source of its warning and cautioned Web site and ISP administrators to be more aware of network traffic on 5 and 6 August.
The warning seems to have been for naught, though, as companies that monitor Web traffic report that ISPs have been unaffected.
Matrix.Net offers tools on its Web site that allow users to check the reachability and packet loss, among other measurements, of ISPs. For US ISPs, no ISP tracked by Matrix.Net is losing more than 2% of its packets for the week, with only two other companies seeing more than 1% of packet loss.
Also, all ISPs tracked by Matrix.Net have been reachable at least 97% of the time for the last week.
Overall, global ISP reachability has not dropped below 99% on 5 or 6 August, according to Matrix.Net's data.
Riptech, a company that compiles the firewall and intrusion detection logs of more than 1,000 companies worldwide to arrive at a picture of the global threat status on the Web, also has not seen any unusual attack traffic, according to its founder and executive vice-president Elad Yoran.
Riptech counts some ISPs, the targets of the attack according to the NIPC warning, among its customers, he noted.
Given Riptech's information-gathering reach, it would detect an attack if one were going on, Yoran said.
"One notion is that this may be a non-event," he said, although he admitted that there may be some form of attack in process that so far has been undetectable.