code injection

HI,

I am using WordPress 4.3.1.

I am seeing some code injected into my page, right below “body” tag. Below is the code :

<em><div class="j_msg">
	<p><a href="[removed by moderator]">kamagra paypal</a></p>
</div></em>

Interesting thing is, that code is visible only when I visit my site thru “private mode”(in firefox) & “incognito mode”(in chrome). When visiting the site in normal mode, that code does NOT appear.

I read various posts which address this issue. I tried the solutions discussed in those posts. For instance :

1. I tried looking for “base64” related code. I am not finding any such code in my site.
2. I tried to disable all the plugins, but still the issue exists.

Can anyone of you can help me out in identifying the problem?