During the last month or so there's been an apparent burst of activity on the Mac malware front.

Fake antivirus software scams have been popping up on Mac screens thanks to what seems to have been effective search engine poisoning campaigns involving Google image searches in particular.

The windows generated by the malicious web pages are becoming increasingly Mac-like. You can see an example at Intego's Mac Security Blog and at Sophos's Naked Security blog (with video). Keep in mind that the names used have varied, and may change again.

Basically, the scam is to persuade the victim that their Mac is infected (eg, with dire warnings and by automatically opening smutty web pages), and that a paid copy of the fake AV software will clean it up. User interaction is needed, so it's not a huge threat - but some people are being fooled.

The other issue is that "The first advanced DIY (Do-It-Yourself) crimeware kit aimed at the Mac OS X platform has just been announced on a few closed underground forums" according to security researcher Peter Kruse at CSIS Security Group. The 'Weyland-Yutani BOT' carries out web injection (ie, it can add content such as bogus form fields to web pages before they are rendered) and form grabbing (ie, it can steal data you typed into web forms, such as usernames and passwords). The initial version worked with Firefox, but Kruse said support for Chrome and Safari would follow.

What wasn't made clear is how purchasers of the Weyland-Yutani BOT are supposed to get the malware onto victim's computers in the first place (presumably via the usual tricks employed to induce people to visit malicious pages), but the existence of kits like this do make life easier for the criminally inclined but less technically able.

There's a tendency in some parts of the Mac community to liken anyone expressing concern about the likelihood of a serious outbreak of Mac malware to the boy who cried wolf. In one way, I think they may be right: the wolf did eventually show up. The difference that when (if) that happens, the boy will be safe but his fellow villagers will be in jeopardy. So I believe the assumption that anyone expressing such concerns must be acting out of self-interest or malice (as did the boy in the story) is misplaced. Yes, there are commercial interests at play, but it would be a mistake to think that's the whole story.

I've practically given up offering advice on this issue. It's become an almost religious matter with little chance that people on either side will change their minds. So I'll continue to take the precautions I consider appropriate, and leave everyone else can do whatever they think is best - which for some is nothing beyond installing OS and application patches when they get around to it. We'll see who ends up worse off.

In early April, Australia-based Pure Hacking stumbled across a vulnerability in the Mac version of Skype that could be exploited fairly easily.

The company did the right thing and reported it to Skype on April 7 without disclosing any information publicly. The response was that the Skype was already aware of the issue and that it would be addressed in the next hotfix. That turned out to be version 5.1.0.922, which arrived on April 14.

But that version was initially only available if you downloaded the Skype installer. If you used the program's Check for Updates feature from the previous version, you were told it was up to date.

It wasn't until the arrival of 5.1.0.935 on May 9 that an update appeared to existing users when they explicitly checked for updates, and a prompt to update started appearing about a day later.

Why didn't Skype take more vigorous action to get users to update the software? According to Skype's Adrian Asher, "As there were no reports of this vulnerability being exploited in the wild, we did not prompt our users to install this update, as there is another update in the pipeline that will be sent out early next week."

So it was just good luck that nobody who stumbled across (or deliberately unearthed) the vulnerability had malicious intent. I don't feel very reassured by that.

Sure, the default settings for Skype mean that you will only receive messages from existing contacts. If someone had developed a worm to exploit the vulnerability, anyone who had changed that setting would have been vulnerable, and then their Macs would have passed on the worm to their Mac-using contacts, and so on.

So will Microsoft's $US8.5 billion acquisition of Skype make any difference? It's not yet clear how closely Microsoft intends to integrate its soon to be new subsidiary. All we know is that Skype will become a division of Microsoft, Skype will Microsoft devices such as Xbox (and Kinect) and Windows Phone, and Microsoft will connect Skype with Lync, Outlook, Xbox Live and so on.

Even though that does suggest Skype will continue to operate as a relatively stand-alone division, it seems probable that updates will be released according to Microsoft's Patch Tuesday practice. That is, updates are held until the second Tuesday of the month and then released en masse. The only exceptions are for extremely critical security updates for serious issues that are being actively exploited.

Without intending to cast aspersions about Skype's current development practices, the introduction of Microsoft's Trustworthy Computing approach may improve the Skype software. Leaving aside the jibes, Microsoft products developed after the introduction of Trustworthy Computing do seem to exhibit fewer vulnerabilities than their predecessors, and those that do slip through are generally harder to exploit reliably.

But back to Skype for Mac: even 5.1.0.935 isn't current! If you download the Skype installer, you'll get 5.1.0.947, but there's no mention (as of this writing) of what's changed on either the Skype security blog or the Skype Garage (Skype's old release notes link now redirects to the latter) of what's changed.

Does it really matter? Not in the great scheme of things. But if you don't know what's changed, how can you decide whether or not to update?

If you have been delaying the purchase of an iMac until the new model arrived, you're probably happy.

Faster processors and graphics are what you'd expect from a 'speed bump' release. An improved camera can't be bad, though I hardly used the camera on my old iMac G5 or my current 27in Core 2 Duo iMac. I suppose it's one of those features that people either consider essential or a yawn - even though most of my family live overseas, I've never really understood the attraction of video calling.

4GB of RAM as standard makes sense to me, but I'm not sure about starting the 21.5in model with 500GB of hard disk space and not offering 1TB as a BTO option. I suppose it'll help push people up to the 2.7GHz version with its 1TB drive, as 500GB goes very quickly in these days of digital media. Also, you need to start with the higher-spec model in either screen size if you want a Core i7 CPU rather than the i5.

I am glad to see four USB 2.0 ports. The three ports on the older models just weren't enough, especially when a USB keyboard was standard. You may need one port for your iPod (etc), another for a backup hard drive (FireWire is better, if you can afford it), and a third with an extension cable or unpowered hub for use with items such as thumb drives, video or still cameras and so on. If you've got a USB TV tuner, that's all four ports occupied pretty much full time.

On that theme, doesn't the single Thunderbolt port on the 21.5in iMac seem like penny-pinching to you? I know it can be daisy-chained, but will all Thunderbolt devices provide a pass-through? For example, Sonnet Technologies stresses that its storage products will, but its FireWire 800 and Gigabit Ethernet adaptors seem to be single port. Since Thunderbolt gives a nominal 10Gbps on each of two channels, it seems unreasonable that any particular device should insist on being the end of the chain.

And it would be un-Australian if I didn't remark on the price differential. The US price of the base model is $US1199. Convert that to Aussie dollars at the current rate and add GST, and that comes to $1218. But the actual price is $1399, or nearly $200 extra. That doesn't seem quite right, especially as we're closer to the factories in China.

At the high end, it isn't difficult to push the price over $3000, especially if you fancy an SSD.

Overall, it's a respectable product refresh. If you were due for a replacement iMac, it's pretty attractive, but I can't see much here that would lead anyone to bring forward a purchase.

The rumour mill is tipping the imminent - as in next week - arrival of refreshed iMacs, supposedly featuring Thunderbolt interfaces and the latest Intel processors.

It's not that this is a hot tip, as a late April/early May release has been discussed for at least a month.

The suggestion is that the new iMacs will look pretty much the same as the current models.

On the other hand, a new look for the MacBook Pro range is being predicted for the 2012 models, along with other significant changes that might just include higher-resolution displays given the news that the developer preview of Mac OS X Lion includes an upper limit of 1024x1024 pixels for icons (compared with the current 512x512), desktop images with larger pixel dimensions than those in Snow Leopard, and an equivalent of iOS's facility for displaying '2x' versions of graphics on models with larger or denser screens.

That's a long way short of the resolution-independent graphics I've been waiting for. I've never been too fond of the way a shift to higher dpi counts on displays has worked to reduce the size of interface elements, especially text, and as my eyesight gradually deteriorates with the passing years it's becoming a bigger problem. (Yes, I do wear prescription lenses, but I'm resisting bifocals for various reasons.)

Changing the display resolution doesn't help the way it did with CRT displays (not that I'm keen to go back to that technology), and Universal Access's Zoom feature gives a similarly blurry effect if smoothing is enabled and a blocky appearance if it isn't.

Being able to say, in effect, "I want 10pt text to have a line height of 3mm regardless of how many pixels the display needs to use to achieve that" would make things easier. And don't forget, the population is ageing.

PS: I can't leave updates alone: the latest is Snow Leopard Font Update which "addresses issues displaying and printing certain OpenType fonts". Those issues have either been a major bugbear or something you may not have noticed at all, depending on how you use your Mac. Perhaps the most common symptom was that PDF files created using Mac OS X may not have opened correctly (or at all) in non-Apple PDF viewers. See Software Update or Support Downloads.

Depending on your hardware and installed software, you may also find an iPhoto update (9.1.2), and a hard drive firmware update for mid-2010 iMacs.

There's been plenty of speculation that Apple is preparing a significant revamp of its online services which are currently known as MobileMe.

Late last year, a purported email exchange between a MobileMe user and Steve Jobs (yes, he does seem to respond directly to customers from time to time) had the Apple CEO saying MobileMe "will get a lot better in 2011."

The completion of Apple's giant data centre in North Carolina fanned the flames of MobileMe rumours, with speculation about features such as cloud-based iTunes libraries with the ability to stream to any compatible device and cloud-based home folders (possibly using a Dropbox-style approach).

Now a discount on MobileMe membership purchased at the same time as a Mac or an iPad has come to an end, and if you search for MobileMe in the online Apple Store the response is "Your Apple Store search request had no matches." MobileMe as a boxed product disappeared last month, so the latter change might just be a sign of the Store catching up to a new reality that the only way to buy MobileMe is to sign up for a free trial and then continue it on a paid basis.

But that possibility hasn't stopped speculation that Apple is preparing to launch the new-look MobileMe within the next 60 days (the free trial period for new signups).

As always, we'll find out soon enough.