This means that a virus or trojan has been auto-detected (rather than auto infected, per the wording of the message).
That network is suggesting that you use the cleaner available at the website indicated, however, there are lots of others that will work just as well, or possibly better.
After you have scanned your system with an up-to-date virus/trojan scanner, you should contact that network via their webpage (if they have one) and check out how to get the g-line removed, or just wait for a couple of days. Most G-lines are removed in a day or two automatically, but if your system isn't clean, then you'll just be g-lined again.
You should also read
this post
