This Q&A is part of a biweekly series of posts highlighting common questions encountered by technophiles and answered by users at Stack Exchange, a free, community-powered network of 80+ Q&A sites.

Depends. Is it Apollo-era code that's running on your Mars lander? I'd leave it alone. Is it 10 year old code written for a 128MB Pentium 2 and it's not medical software? I'd probably have a poke at ...