The Sysbug-A virus has been set loose and is attacking "the usual suspects" - meaning that Microsoft Windows users should be on alert, according to one IT security company.
According to security provider WhiteHat, those vulnerable to the virus include anyone using Windows 2000, Windows 98, Windows 95, Windows ME, Windows NT and Windows XP.
Chief security officer at WhiteHat, Tom Slodichak, said that Windows users were most often picked on by virus writers simply because of the sheer number of them out there.
"If something like 90 to 95 per cent of the world's desktop users are using Windows software both in the enterprise and at home, you are not going to go after small pockets of unusual operating systems," he explained.
Slodichak described Sysbug-A as a classic email virus which originated from an account called James2003@hotmail.com.
"It's always the same subject line - 'Re: Mary' - and the email claims to have a zip file of photos of a tryst and tries to get the user to click on it and open it up," Slodichak said. "But it includes an executable that drops a Trojan onto that machine which will enable some unknown party to potentially take full control of that machine at will."
He said that a user wouldn't realise that his or her PC had been taken over immediately, but because the virus releases an unauthorised program or Trojan, the virus writer would have full access to the machine as if he was sitting at the infected computer himself.
"The Trojan doesn't cause any damage to the PC immediately," he said. "It doesn't erase files, it doesn't cause any misbehaviour that the user can detect but Trojans have been implicated in denial-of-service attacks or distributed denial-of-service attacks such as those on Amazon and eBay a couple of years ago."
There are both proactive and reactive measures that can be taken to fend off viruses, Slodichak said.
These included deleting suspicious emails that come from unrecognised sources or that have subject lines that simply don't make sense.
Most importantly, however, users need to perform constant virus checks.
"In other words, have an antivirus program installed," he said. "Generally speaking they are about $US50 per year depending on the subscription and now there are also automatic updates whenever a new [virus] signature is available."
Slodichak said that although virus writer "villains" were getting more sophisticated in their work, there was currently no new "radical technology to detect or cleanse machines of viruses".
He said that the old and reliable technology that was used today by matching incoming messages with signatures was still the most effective way to fight viruses.
"The industry is looking for means of detecting viruses without having that signature updated to your directory, but nobody's come up with any sort of viable technology yet," he said. "So, that's the one weak link. You have to have your antivirus and your auto updates up if up if you want to be assured of antivirus protection."