Do I have a virus, a back door? Am I hacked? Recently my MacBook has slowed down a lot, though I haven't downloaded any large files or installed new applications, I've mainly used the web.

Yesterday I was doing some work in Photoshop and noticed I had a terminal window open. So I open it to find it continuously pinging 25.212.254.172, as if it was trying a DDoS attack or something. That's when it freaked me out. 

I've deleted a whole lot of unnecessary files and applications taht have been on my laptop for the longest but I'm still unsure what to do. A lot of people argue Macs don't get viruses and I think that's a load of crap. 

How do I protect my MacBook, manage outgoing connections, remove viruses or figure out what's going on?

Oh and I had this weird thing happen...

I was traveling to Las Vegas two weeks ago and my MacBook looked like it was opened from the bottom and tape was hanging out of it - after retrieving my luggage from the airport. I'm thinking of opening it up but what would I look for if I'm being monitored through hardware? Any tips here too?

Yea I know I'm a bit paranoid but you can't blame me with the NSA revelations.
I don't know who you are, but chances are, you're aren't relevant enough to warrant hardware tapping.
Macs don't really get viruses. There are some trojans (malware in disguise as user software), but they require the user to manually input their administrative password. If you're suspect your infected, try a virus scanner like ClamXAV, but I doubt you'll find anything. Apple does a really good job at keep up to date against malware. DO NOT install any sort of on demand virus software. Generally Mac anti-virus programs don't actually protect from Mac viruses; they're meant to prevent Macs for being a vector for Windows viruses. As a Mac user, it's very easy to download a file infected with a Windows virus, and unknowingly pass it on to a Windows user.
A much more likely explanation is some sort of system related issue. Can you please keep Activity monitor open, and enable its dock icon CPU viewer from this menu:

Keep an eye on the CPU levels, perhaps you'll find a runaway process that's using your system resources.