Little green hackers

If you've seen the film Independence Day, you'll know that the Earth was saved by Jeff Goldblum's geeky scientist character inserting a virus into the main computer system of the alien mothership. In addition to Goldblum, we clearly have to thank Microsoft's marketing team, as, remarkably, the aliens appear to be running a variant of Windows on their server (as my colleague Susan Stepney has highlighted), making them vulnerable to attack.

Of course, this is just sci-fi licence, and nobody seriously believes that even Bill Gates has managed to achieve intergalactic penetration. Or has he? Richard Carrigan clearly thinks so, as he's recently raised concerns that the Search for Extraterrestrial Intelligence (SETI) may run the risk of inadvertently introducing alien computer viruses into our global computer network. His forthcoming journal article (subscription might be required) describes his "SETI hacker" hypothesis in rather more detail.

I'm sure Dr. Carrigan is trying to make an important point, but I'm afraid it's somewhat undermined by the implied understanding of how operating systems and viruses actually work. To quote from his article:

At least two scenarios need to be considered in protecting against a malevolent SETI Hacker signal. One is a computer virus in the message that takes over the computer at the receiver. The other is an open message that gives an impenetrable software code or instructions for a hardware translator to handle an opaque message. Both cases are dangerous. The damage may be done before the receiver appreciates that it is under attack. This is the current experience even with Earth-based hacker attacks. There may not be an opportunity to pull the signal out of the computer or turn off the power before the intruding signal has taken over.

Computer viruses can only "take over a computer" if

• They are written in the native machine language of the computer, or are present in some other "executable" form (eg. a macro),
  
• They are then actually executed
  

Even if the signals being decoded by SETI did contain an alien virus, it's extremely unlikely that it would encode executable code that could infect a human-constructed machine. Even if it did, we would still have to then knowingly run it, so I think we can safely rule out alien hacker attack in the near future. However, I have an open mind, and will happily reconsider the possibility of inter-stellar crime if (for example), I receive an email from Councillor Zarg of the planet Cthu-Targ9, asking for my absolute discretion in transferring 3.5 million Galactic Credits from his father's bank account...