Probably the worst that will happen is that you may get spam (or more spam than before).
You could change your email address - but that may be overkill.
You'll be surprised how easy it actually is to live with spam. My email addresses are knocking about all over the place (for various reasons) - and I live with that.
You email provider may already offer some spam protection.
Presumably you already have good AV and malware protection anyway - so no harm should come to the system as long as you have good ones, and keep them updated.
I doubt if 4 hours was enough to get your email harvested by spammers anyway - but you never really know.