[abathur]

There's no way to obtain and execute source code that you didn't write and hand-compile for which this risk doesn't exist. (And it applies in its own sense to books, paintings, phone calls from mom, letters from an old mentor, DVDs, rental cars, ...)

[heavyset_go]

Download, verify keys and signatures. You could run a checksum or even read the code yourself depending on how paranoid you are. Otherwise, you're just hoping mycrimepics.net/dontsnitch wasn't subpoenaed between your last visit and now.