When you have already used "the dog ate my homework" and "my baby sister pulled the plug just when I was about to save", try the latest excuse from Fermilab: "an alien virus from space hacked into my computer".
In summary, a researcher at Fermilab warns that the risk that aliens would hack SETI is "non-zero".
Seriously, though: If, for argument's sake, we assume that intelligent life on another planet only 25 light-years away registered our first television broadcasts 25 years ago (with a 25-year lag, mind you), and immediately decided that the progenitors of I Love Lucy must be annihilated, what are the chances that, in 1980, they were able to predict (again, mind you, based on information only up to 1955) that in 2005, we would be using 32-bit Intel processors on von Neumann architectures, let alone the details of, say, the current version of the Win32 API? And if they were able to predict (or guess) that the SETI client were vulnerable to a particular stack-smashing attack before any hacker here on Earth, would they be able to pull that off within the first few packets we received from them, before we would declare SETI a success based on the appearance of coherent signals from their planet?
We leave our tinfoil hats outside the lab, thank you very much. (Good thing it's shielded, though!)