Which was the year the linux distributions, windows have first used to sign their updates? Historical question that is hard to "google".
In recent releases, Debian has been using strong crypto to validate downloaded packages. This is commonly called "secure apt" (or "apt-secure") and was implemented in Apt version 0.6 in 2003, which Debian migrated to in 2005.
Although work for the underlying dpkg-verify had started since 2000.
Windows is a bit difficult to research. There are evidence that Windows 98 had support for signed hotfixes:
Installing Windows 98 and Windows 98 Second Edition Hotfixes
... To install a Windows 98 and Windows 98 Second Edition hotfix on a single computer, run the self-extracting installer. This installer performs the following actions:
- Unpacks the files that are needed for installation into a temporary folder. Typically, these files include:
- A digital signature file (.cat) used to digitally sign the hotfix binary files (in most situations).
However, I'm not quite sure what Microsoft means by "in most situation", perhaps it doesn't always require hotfix packages to be signed?