The warning, carried on the main page of the RockyMountainNews.com, said:

"If you visited RockyMountainNews.com between Saturday and Tuesday on a Windows computer without virus protection or have not updated your virus protection in the past two weeks, your computer might be infected with a virus."

The warning on the Denver Post main page said:

"If you are using a Windows computer, do not have virus protection or have not updated your virus protection in the past two weeks, and have visited the denverpost.com homepage between last Saturday and Tuesday, your computer might be infected with a virus."

A link to information on the virus is included in the warning and that page classifies the virus as "a keylogger program that can capture all user keystrokes (including confidential details such username, password, credit card number, etc)."

The same warning was also displayed on www.postnewsads.com/jobs/ and a Google search contained the warning, "This site may harm your computer."

The virus operates on Windows systems as wllamek.exe and installs "a module that is loaded into the address space of every running application," according to the Web site linked to in the notice.