Virus on blog?

First, try:
– deactivating ALL (yes all) plugins temporarily to see if this resolves the problem (plugin functions can interfere). If this works, re-activate them individually (one-by-one) to find the problematic plugin(s).
– switching to the unedited default Twenty Fifteen theme for a moment using the WP dashboard to rule out any theme-specific issue (theme functions can interfere like plugins).
– If the issue still persists, try scanning your site: : http://sitecheck.sucuri.net/scanner/

For questions regarding this theme, I recommend asking in its dedicated support sub-forum. There you will be more likely to find a good answer from its developers/users at:
https://wordpress.org/support/theme/zerif-lite