I find it hard to believe that someone would go to the trouble of hacking into his laptop just to steal his AW details to then send malicious messages to his regular.
If it was me? My first port of call to fall under suspicion over these sort of shenanigans would be the regular.
Or her pimp. Prossies, unless they are the techie variety, can be very lax with their stuff. Bear in mind they will often get a pimp or boyfriend to do their AW webpage, so he has their login details and access codes. I did one for a reg a long time in the and urged her to change the codes afterwards, just so if she got screwed I couldn't fall under suspicion. She stressed that she trusted me completely and implicitly. She also trusted her ex 'implicitly and completely' it seems, though forgetting she might have changed her mind after dumping him. Never let a prossie log on with your gear (it can produce a fake alias on your account) or use hers to log on.
There have been a number of claims of AW being hacked but I've not seen anything official, probably hasn't happened. I'm sure mumynuts would love to get access, as would anonymous (they've tried to 'bring down' UKP in the past and failed).
Security basically comes down to, 1) who and I protecting 2) what information from and 3) what are the consequences if they get it. Each level of security engages different levels of hassle, so just work out what you need for your circumstances is the golden rule. But not opening attachments from unknown senders is another golden rule, for everybody. Wikileaks have just released details of the CIA's root hack for Mac devices. In 2008 they needed physical access to install Nightskies: things may have moved on. Once the exploit is discovered history suggests others will follow where the CIA leave off. However, if your only concern is to avoid your wifey knowing or a prossie targeting you, such high-tech hacks seem unlikely. Google, of course, keep all your browsing data, private facility (Opera) or not. If you need private browsing, DuckDuckGo or Disconnect are standards (which you can access from a normal browser). A Tor Browser goes a bit further, with or without the addition of a VPN, but using a VPN when you don;t need it has its own downsides. It can temporarily disrupt your wifi or your ISP (who can see you are using a VPN in nearly all cases) may strangle-reduce your data speed.
This is all standard knowledge, but if you want to post tips, please put them on he off-topic if you have access as that's less public (or send them to a member who has access).