Can hackers get into your blog through your theme?

[Ajebo25]

I have heard about this on Facebook many people say that using nulled theme for your blog isn't good that it may contain codes which may give hackers way to get into your blog but I don't think this was true what made me suspect that what they said was true was when I downloaded a nulled template for my blog which is hosted on blogger, when I tried to edit the HTML code I found some codes which someone placed in the templates HTML code this code will give back links to sites in my HTML code without notifying me.

So if they can do that and it works what is the assurance that they can't hack into a blog just by editing the themes HTML code I want someone to clarify this for me if a blog can be hacked just by using a nulled theme or template?