Microsoft detected the Win32/PSW.Lineage.DN/PWS-Lineage virus on your computer

Had a game called Air Conflicts installed on my PC (Vista Home
Premium) and it worked very happily, I got bored with the game and
removed it.
Have had some young relatives staying so decided to re-install it for
them. It installed fine but when I try to use it I get "ac.exe has
stopped working" followed by a message from Microsoft saying

"Virus alert: Microsoft detected the Win32/PSW.Lineage.DN/
PWS-Lineage virus on your computer

This problem was caused by Win32/PSW.Lineage.DN/ PWS-Lineage, a known
computer virus.

Solution

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To prevent this problem from occurring again, install and run an
up-to-date antivirus program on your computer.

Additional information

For more information about computer viruses, go online to the
following Microsoft website:

Protect your computer: Beyond the basics

To keep yourself informed of the latest security issues, go online to
the Microsoft Security website:

Microsoft Security

To see a list of Microsoft and third-party solutions for spyware,
adware, and antivirus software, go to the following webpage online:

Security software: Downloads and trials

Tip
You can avoid this and many other errors by running Automatic Update
and running an up-to-date antivirus application. Automatic Update
keeps your computer up to date and secure by notifying you as soon as
updates become available.

Learn more about automatic updating

With automatic updating, you don't have to search for updates or worry
that critical fixes for Windows might be missing from your computer.
Windows automatically checks online for the latest important updates
for your computer. Depending on the settings you choose, Windows can
install updates automatically or just let you know they're available.

For more information about automatic updating, go online to read the
following article:

Windows Update Frequently Asked Questions


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I am running NOD32 which indicates no problem and neither does
Malwarebytes.
The install was from the same disc as my first install.
Googled for an answer but only found other people with games getting
the same message.
Any solution greatly appreciated !!
TIA